International System of Units overhauled in historic vote | Hacker News Reader

International System of Units overhauled in historic vote

npl.co.uk

834 pointsdaegloe575 comments

See, the US wasn't being stubborn in not adopting metric, it was just waiting patiently for it to progress from beta to 1.0. :)

(Fun fact: all the US customary units have been officially defined in terms of their metric counterparts since 1893: https://www.nist.gov/sites/default/files/documents/pml/wmd/m...)

So it's fair to rib my American friends with the fact that Imperial is implemented using metric?

I like to commend my American friends for their undying loyalty to the memory of the Empire. U.S. customary units are derived from units that helped the British conquer the world, but even the British themselves have shamelessly abandoned them for the units of a filthy, monarch-less republic. It's good to see that Americans still subconsciously yearn for the firm ruling hand of their rightful Queen.

Note: Americans hate it when I do this.

Our King wears no clothes. We desperately could use a Queen and some manners right about now.

It just doesn't have the same ring to it.

"He won't move an inch," or "He won't move a centimeter."

"She won't quit until she's six feet under," or "She won't quit until she's two meters under."

"I'll go the whole nine yards," or "I'll go the whole nine meters."

"You can see for miles and miles," or "You can see for kilometers and kilometers."

Yes, that's true. Another argument my American coworker had put forth: "American rock-n-roll needed Imperial units... or the lyrics would not work".

In case you are not joking... in metric countries we still say the same sentences you say, with miles and inches. That doesn't mean we use the olde units to actually measure something...

Well, then you are welcome for us keeping the more poetic units alive and meaningful.

Sorry, but no. They are just our old units that stuck in everyday language. They are probably not even closer to yours than yours are to antique Egypt ones, given that they were not internationally standardized and merely referenced the same body parts.

And we have expressions including other old units that you don't have (lieu, arpent, toise, etc.).

Not really --- in some languages these sayings actually are already in metric units. The SI system is by now over hundred years old, so just by waiting probably will upgrade unit system also there.

I think there's a serious point to what you're saying. I was bought up in the UK so I have metres for short distances and miles for long distances. If you say to me 5 miles I instantly know what you mean. If you say 8km, I have an academic understanding but not really an intuitive feel for what you mean (other than 8km=5mi, feel 5mi).

That's just familiarity though. People in countries that primarily use kilometers have the same intuitions about them.

I doubt that in practice an average person would be able to (reasonably) accurately differentiate between 4 miles and 5 miles or 6km and 8km without external measurement tools in an unfamiliar environment.

The heuristics at play that the human brain would use is likely: "5 miles is way more than I'd normally want to walk on my feet, since the trip would take me about 2 hours."

I need you to understand that those phrases are still used all the time in English speaking countries that have adopted the metric system.

Changing your scientific measuring system doesn't necessitate a change to your colloquialisms; commonly used phrases don't change.

As our metric British friends say at the end of a long day: "Ah, I can't wait to get down to the pub and have my hard-earned 568.261 ml!"

In Russian you still have people using colloquialisms and idioms with units that were put out of use almost a century ago, yet everyone here gets the meaning (or at least the intent, which is what matters in the contexts they are used in) since they have stayed in the literature written centuries ago and of course nobody went out of their way to fix measurements in works of fiction.

Heck, most people using them don't even have a rough idea of how much they originally meant, and if you were to press them to give you a number for the sake of an experiment, they might be 2 orders of magnitude off.

https://en.wikipedia.org/Obsolete_Russian_units_of_measureme...

That's some well metered ribbing. No worries. We can take it.

> metered

Ah!

*British themselves have shamelessly abandoned most of them, most of the time, when convenient

Your friends don't like it when you invent reasons to antagonize them? How odd!

I was born and raised in the US and I don't think I've ever met someone who has any sort of complex about the British Empire, or who would be any more insulted by "you should be ruled by the Queen" than "you should be ruled by the President of Uruguay" (or any other random country). The US was last part of the British Empire before most of our ancestors came to this country.

Honestly your comment, assuming it is meant to be taken seriously, strikes me as bizarre, and I suspect you're misinterpreting your American friends' reactions.

But Brits haven't completely abandoned them, have they? Maybe for educational, scientific and in manufacturing industries it's all metric but they still seem to use a blend of imperial and metric for day to day stuff. The distance is in miles, speed in miles/hr, they use lbs as well and deg.F from time to time (mostly deg.C tho),"pints" for beer, ft and in for height etc.

Nope, because we don't use the Imperial system, though. We use American Standard Units. They happen to be just like the Imperial units, except they have more freedom.

As of today, they are both implemented using fundamental constants. ;-)

But indeed, most people worldwide are surprised when you tell them that there is no standard inch or standard pound sitting in a vault somewhere. Most machines, and most design software, have a button that switches between US and metric, and the machine itself doesn't care. More and more new products in the US use metric fasteners unless it's for something where a standard applies to exactly one thing, such as spark plug thread. I have used my metric tools more than my US tools in the process of doing repairs around the house, on my car, and my bikes.

One fastener on my bike uses Whitworth threads.

For all intents and purposes, it has ceased to matter.

Only if we can rib on you for using imperial machining standards and imperial pipe thread forms.

Now can we redefine 1 pound to equal 1 kg?

(the opposite of https://xkcd.com/2073)

Considering the speed at which metrologists create new standards, we'll be about three iterations into the infinite loop by the end of the century.

Can you imagine the confusion? Having the same word mean a different amount of something would cause a lot of misunderstanding. Saying "This car weighs 2200 poundsm" have two different meanings depending on the year you said it sounds awful.

The new metric definitions work because they don't change the actual amount, they just change the way the amount is defined. (Natural constant vs reference weight)

See ton vs tonne

We could gradually redefine pound to be closer and closer to kilogram, say, over a century, so that people don't notice. ~

That sounds like it would require more coordination than just adopting the kilogram as the primary unit of measure in a short period of time.

Nope, 1 pound should equal 0.5 kg.

It does in France already and has done for years, so when you ask for a pound of cheese you get 500g. Simples.

I'm one of the weird people that actually really likes imperial units. For instance:

1 foot -- base 12. This is a superior base to 10. It can be easily divided into 4ths, 3rd, and 2nds. Base 10 can only easily be divided into 2nds.

1 inch -- an easily identifiable unit of measure for smallish things. About the width of my thumb. A pretty good unit.

For low precision, inches become 1/2, 1/4, 1/8, 1/6, 1/64, etc. Each one is half the size of the previous one. I actually like this one a lot. An eight being half of a quarter is a really easy way to work with things when you're building stuff. Think about drilling a bolt hole in the center of a piece (half the width), or drilling two bolt holes with something in the center (divide those halves in half again) etc. Fractional is really good for building stuff.

For precision: thousands of an inch. Harder to visualize, but precise (has the same problems as mm imho). Millionths of an inch when you get into serious metrology.

Okay temperature: In imperial units:

0 = REALLY cold. 100 = REALLY hot. 50 = somewhere in the middle. Put on a sweater, but not dangerous.

100 = about the temperature of a human body.

Water boils at 212F and freezes at 32F. There are 180 degrees (degrees!) between freezing and boiling. 180 is, again, base 12. It's the 15th order of 12.

I actually love imperial units. I greatly prefer them to metric (even though I do use metric very frequently, and can see the appeal). I think I just actually prefer base 12 to base 10.

I also think that F is seriously superior to C.

You are definitely (and thankfully) not the norm. Imperial units are awful. They're more ... human, maybe, in that a foot is about one human foot long, and that an inch is about one human thumb width, and how 0F feels "pretty cold" and 100F feels "pretty hot", and to me the charm of imperial units begins and ends right there.

Those are literally the only redeemable qualities about imperial units, and they have nothing at all to do with their utility as a tool for measurement.

I am glad that you like them. Use them all you like. I won't.

What are the redeamable qualities of metric units?

It’s based on the decimal system, which we happen to use in our primary numerical system as well?

We use the decimal system for imperial units too. Thousands of an inch, millionths of an inch, etc.

In most practical applications that I've seen fractions of imperial measurements used, it tends to be in powers of 2, i.e., 3/16 inch, 1/4 mile, etc. Decimals can certainly be used, but for most applications where you'd use something like a "millionth of an inch," it's vastly more common to use metric.

What applications are you talking about? Just for a general example of the sort of thing I'm talking about: https://youtu.be/EWqThb9Z1jk?t=137

They're resurfacing a surface plate, which has to be very flat. If you listen to the exchanges between them, everything is being done in millionths of an inch.

In my experience (electronics manufacturing), both PCBs and machined parts are usually in mils or decimal inches, although millimeters are becoming more common and many drawings show both systems.

This might be specific to where you live though, in my experience in the electronics industry, I've pretty much only seen millimeters.

Or nothing is stopping you from using things like 1.3 inches, 2.7 miles, .6 gallons. I tend to use the fractions when doing measurements in my head. But if things get too complicated and I have a calculator I switch to decimal.

Frankly, while mathematically speaking 12 is a great base, people don't think in twelves - you can quickly perform arithmetic and our entire education system of math relies on base 10. Kind of hard to suddenly add two fingers to everyone. Additionally, base 12, would not act like 12 does in base 10, thus if base 12 is your key point of reference, a foot should be 10 in base 12 for inches.....

People don't really think in terms of 10s either - that's just societal conditioning based on the usage of fingers to count. If you can accurately picture 1/3 of set, but your number system cannot, it's not really that accommodating of a system.

By the way, you can count base12 on your hands using the digits of your fingers. We just teach kids to use fingers because it's the norm.

Why are you so obsessed with thirds? If you care about short, clean fractions on a human scale, base 6 is overall better, see this table: https://youtu.be/qID2B4MK7Y0?t=992

Plus you get all the convenience of having five digits on a hand and 5 as the highest counting digit, so you can count to 55 on two hands, and all the rest of the benefits in that (totally serious) video.

A numbering system based on human fingers would be base6.

You've got it backwards. Counting to ten on your fingers predates the concept of our modern positional number system by hundreds of thousands of years. That's why base 10 was already the well-established natural choice when that system was invented.

Thinking that you could represent the quantity IIIIIIIIIIIIIIIIIIIII by the string "21" because it's 2 * 10 + 1, or similarly as "three fingers on left hand, three fingers on right hand" seems obvious to us now, but is actually pretty recent technology relative to the whole timescale of human development

I'm not sure what your point is. A numbering system based on five-fingered hands is still base6. It doesn't make mathematical sense to argue that we learn base10 today because our hands have 5 fingers. Even if you argue that we have 10 total fingers, that's base11. Does anybody advocate that? How did we come to such an arbitrary thing as base ten?

No, counting on the hands is not base anything, because positional number systems did not exist. Just like Roman numerals or tally marks aren't base anything.

People counted on fingers like with tally marks - they could express the numbers one through ten. Thus ten became an important and familiar number to humans. Thus it would have seemed natural to use a base 10 number system many millennia later.

Additionally, base 12, would not act like 12 does in base 10, thus if base 12 is your key point of reference, a foot should be 10 in base 12 for inches.....

I honestly cannot make any sense of this part of your argument. The symbols 10 would only look like ten they would still mean a dozen and the properties would remain the same. Furthermore people don’t think in twelves because we are not taught in a dozenal numbering system. And there is no need for twelve fingers it would be a simple thing to create two additional hand symbols to teach children to count to a dozen.

Twelve is a great base. I would prefer it but it isn’t the sort of thing that can be changed.

He is saying that you need twelve digits to actually use base 12 and that in every base N with N>1 you write N as 10 (eg in hex 10 is A and 16 is 10)

Understood, his mistake was this “base 12, would not act like 12 does in base 10". That statement is mistaken. A dozen would look like ‘10’ but it would still behave like a dozen.

Clearly, people do think in 12s, because it's been a common thread in mathematics and measurement and calendaring through many different cultures going back to the Sumerians.

Let me clear something: how do you count? Can you multiply 63895 by 12? By 6? By 3? By 10? This is an standard, there have been coltures where the base was 60 and they could multiply 63895 by 60 easily. But now the whole world counts in 10.

I would be happy if that number was 12 but the simple fact that we write in base ten makes it not the case (also mathematically speaking 12 is divided by a square which causes weird things)

There is nothing wrong with 12 but as long as you cannot do 63895*12 easily 10 is better

They're globally standard, decimal, and internally consistent. One never needs to wonder how many meters in a kilometer or how many grams in a kilogram. They have some human usable qualities as well; it's convenient that water freezes at 0°C and that a kilogram of water is also a liter.

a kilogram of water is also a liter

I have never, in around four decades of living, had an actual need to determine the mass of a given volume of water, or the volume of a given mass of water.

When cooking, I routinely need to split some quantity of an ingredient into thirds or quarters.

Yet I am also constantly told that I'm ignorant and backwards and irrational for preferring a system that optimizes for the latter, rather than for the former. Base 12 is genuinely better for many real-world applications than base 10, those applications are more common in the lives of non-scientists than the applications metric is optimized for, and I doubt you're going to be able to produce a rational argument otherwise.

So you never went hiking for a longer period of time or did anything that actually involves carrying water.

I remember when some guys thought about building a pool on the balcony, calculating how much water weighs is admitably not ver often used, but when it is the consistency of the metric system is nice.

I work with wood in mm for years and never had any problem with the metric system. Finding the third, fifth or sixth or whatnot is not hard if you are used to it at all. Converting from mm to meters isn’t hard, etc.

Having a number like 666.66 mm probably sounds scary to measure (beyond the religious connotations), but in fact it is a point on a line that is easy enough to find.

But that's because your recipes are built on the easy divisibility, no? If your recipes are built on weight measurements, suddenly "easy divisibility" brings nothing to the table. If you cook with a kitchen scale, "one ml of water is one gram" is used all the time.

> When cooking, I routinely need to split some quantity of an ingredient into thirds or quarters.

Why?

Recipe feeds six. Making it for two.

Recipe feeds five. Now what?

Never seen it. Have You?

Yes, but I live in a country which uses the metric system.

Makes sense. People respond to the systems they live with.

Are they globally “standard?” China uses Mou to measure land area. A pyeong is used in Korea for housing floor area, the British use pints in the pub and stone when weighing themselves. The US uses feet and pounds. We use clocks that have 60 seconds, 60 minutes, 24 hours, weeks, months. If we want to be consistent, “minutes” should perhaps be 100 seconds, for instance. Horses are measured in “hands.”

“Global standard” isn’t necessarily an argument for “good.” Why aren’t imperial units the standard? Who actually decided that metric was the right answer?

And as a previous poster mentioned; why don’t we say a megameter or gigameter when talking about long distances? Because ultimately measurement units are really about human understanding, despite ostensibly being “scientific.” A foot as just as scientific as a meter. NASA went to the moon with imperial units and it worked out just fine. People and countries are entitled to their preferences. We don’t advocate English or Chinese to be the global standard language. Or that all countries use euros or dollars. Weights and measures can be perfectly accurate regardless of the units used; the idea that we should either create or adhere to a global standard is not unlike suggesting everyone speak the same language.

> the British use pints in the pub and stone when weighing themselves.

Using a country that excels in being contrary, to the point of being the national pastime, is a poor example.

Even then we literally use metric for everything else. And although it is referred to as a pint, it is measured in metric.

Weighing yourself in kilos is a more modern thing, but that is really the only thing.

There's a reason measurements have a global standard, NASA attempted to work with a team from elsewhere that used Metric, and this lead to the loss of the Mars Climate Orbiter when they couldn't work well together and had a conversion problem.

Standards make it easy for people to work with each other across borders, and most of the world uses metric already. NASA has since then started all of their new projects on Metric too.

I do agree with your point about the fact that weights and measures can be accurate regardless of the units used, the argument against Imperial isn't about accuracy, it's about ease of conversion and changing bases of the unit scale. (Like 12 inches to a foot, but 3 feet to a yard etc)

> Who actually decided that metric was the right answer?

People who wanted actual definition of units.

Once upon a time if you wanted to sell stuff in my home City you would need to use the city measurements made via a really big stone tablet in the old roman center with various units of lengths.

This was hard to communicate and stuff.

The French decided that one unit of measurement was better than many and made one "easy" (possible) to replicate and validate when the imperial one still used medium sized wheat seeds as measure of pressure.

But now everything is ultimately standardized on the metric system (even the US).

So one need to ask better at what? Better to standardize? Metric no doubt. Better to use? Well this appears to be controversial

Global standard doesn't mean that every person everywhere uses metric. It means that people everywhere can use metric and they know what it means, and that official weights and measures are done in metric. Use whatever glass size you want at the bar, or measure your horses however you wish, but when you get on the road the signs are in km/h.

Plenty of people are "bilingual" with metric and local. Canadians are universally bilingual with metric and imperial. It's not that hard.

The metric prefixes we know and love are a huge plus. If you convert from Volt to kV or to mV, you just need to move your comma. Ah see what I did there? I uses a metric prefix on a unit that is also used in the US.

The thing is 1V is also 1Nm or 1J or 1Ws. So suddenly we have the meter there right besides the Newton. In fact if you look beyond "I build my own shed in the US"-scenarios, you will find the meter everywhere intertwined in the definition of other units. In fact the definition of imperial length units is based on the metric definition of the length light travels through vacuum in 1/299792458s. So the foundation of the meter is light speed, which helps with all kind of practical issues in physics.

The metric system has maximum compatibility to all these unit systems (except the °C which is a more-practical-for-every-day-use offset version of Kelvin).

Unit systems are always something you grow up with and are therefore an emotional topic. People will take fractions of inches as an example of how metric fractions fail to deliver, when in fact no european woodworker has even remotly a problem with doing their thing in mm. In front of me lies a ruler with a 0.1mm scale and a caliper with 0.01mm or 1/128In accuracyIf I really wanna be ±0.01mm accurate on a cut of 1/3m or 333.33mm getting that accuracy would not be easier in inches. My saw blade is precisely 2mm wide anyways..

V=J/C

V*C = J = Nm = Ws

>They're more ... human, maybe, in that a foot is about one human foot long, and that an inch is about one human thumb width, and how 0F feels "pretty cold" and 100F feels "pretty hot", and to me the charm of imperial units begins and ends right there.

As far as we know, humans are the only thing in the universe that care about any of this stuff. A computer couldn't care less if you are using 1 foot or 0.3048 meters.

Why not optimize for humans, the things actually using these things? Optimizing for the computer just seems...silly. It seems like something somebody from the 1970s would have thought was a futuristic idea.

Also, the statement that metric is more useful for measurement largely ignores the fact that Imperial has stuck around so long because of its usefulness in trade work.

It's definitely ONLY because of base12, but being base12 - imo - positions it far beyond metric for daily use. There's a reason why food items so commonly come by the dozen. Why would anyone prefer to build a house using a system that can't even accurately measure 1/3?

1/3 can easily be measured in metric... it's just not a whole number.

Far out I can invent a system that is unique to everything, and I can create my own abominable conversion ratios all I like. It doesn't make the system superior, it makes my system necessarily inferior.

My TV is now 12 Settos in size. My surround system consumes 12 audots of power. My fridge holds 12 cubic fudo of room.

There. Now everything is easily divisible by 12ths.

I won't even go into conversion factors on this insanity.

Metric is objectively the better system to anyone that doesn't have a decades-long familiarity with the stupidity that is the imperial system. That's coming from an american without a college education, by the way. I am the target demographic for the pro-imperial people. I wasn't abducted into any metric-only education system and forced to convert or fail and disappoint my family. I was a disappointment by my own hand, thank you very much.

I challenge you to make a 1/3 cut in meter length wood using a metric ruler. Must be accurate to 1/128 inch (0.2mm), the tolerance used in fine woodworking.

Not only is it trivial to just cut at 33.33 or what have you, your argument breaks down at cut it into 1/5s.

Good luck with imperial. And has to be accurate to .02mm. In metric? This is a no brainer

That doesn't really hurt the argument at all - you're just arguing about factors now, and if you're really going to go there, 12 wins due to having more factors. The mathematical correction you'll have to do to measure 1/5th will be displaced by all the correction you don't have to do for other cases.

You're bent on the whole number thing. Why?

Whole numbers don't make things easier to measure or cut or reason about. I can measure in thirds or fifths of a meter or a foot or an inch or any unit you want with a compass and a straight edge.

You're arguing that the mark on the tape measure is possible for imperial and impossible for metric, when thirds are involved. Not true.

Because infinite numbers are not a natural expression of discrete measurements, and when it comes to being price 1/3 = 4 is always going to be easier to put your finger on than 1/3 = 3.333.

I work in software and data analysis in the construction industry. A continuous measurement is good for some things, but it's definitely not good for discrete measurements. Furthermore, a lot of the people who work in the field for construction greatly prefer Imperial for a reason. They have no bias towards systems beyond what works fast and easy.

"price" is an autocorrection of "precise"

> and when it comes to being price 1/3 = 4 is always going to be easier to put your finger on than 1/3 = 3.333.

Am I missing something? Wouldn’t it just be putting your finger on the 10 cm mark? This is approx 4”.

I realize this is not exact conversion, but it’s trivial to come up with examples where metric is easier: say you have a piece of wood 7 7/8” long that you want to cut in half. Is it easier to put your finger on 3 15/16” or 10 cm?

What is stopping people from making meter sticks with 3000 lines, i.e. every third of a millimeter is marked?

(The point is, there is nothing any more "infinite" about the rational number 1/3 than 1/4, 1/5, 1/2 or what have you. It just can't be written in the arbitrary base 10 system, just like 1/5 can't be written in base 12)

There is nothing stopping you from writing 1/3 meter.

I work a lot with wood in the metric system and the third thing is bot a problem at all. I never had even remotly any trouble finding 333.33 mm or a 666.66 on a tape measure. For anything that needs extreme accurcay I’d go with my iron ruler with 0.1 mm ruling and beyond that I would go for a caliper.

If you consistently have to use a weird measurement over and over again, you usually end up making a temporary ruler (paper, wood, metal) anyways

The factor argument is not really something that stands up, because you need to consider factors for an arbitrary length of something in the world, not a well defined unit of your own making.

How about 1/3rd of a tree? It's likely to be in some ungodly fractional amount of an inch, that's extremely hard to convert into feet, but in metric the decimal system just makes it super easy.

Can I pick the blade thickness?

Sure, kerf is less important than the thickness of your pencil line in terms of accuracy

wasn't going to use a pencil

Place the center of your line at the correct location.

You're missing the point if you don't see the problem of an infinitely repeating measurement. That doesn't translate to a tangible action. You can't cut 1/3 of a meter, and there's no subunit to roll down to that can express the right number. It's not like Imperial system exists for uneducated people - it exists for trades people. Metric is the "simple" system, because it ties back to 10, a number we're all used to. I like the metric system for its scalability, but as somebody who works in a math-y area of computing, I have nothing but distaste for base10.

I can cut 1/3 of a meter just as accurately as you can cut 1/3 of a yard.

Not being a whole number does not make it harder to find where it is.

Ha! I'm happy for your apparent virtuosity, but the whole of America's construction industry is quite a few years into disagreeing with you.

So THAT'S why U.S., Liberian and Myanmar architecture is centuries ahead of the rest of the world.

By the way, why isn't your currency base 12? All the purported benefits that apply to length would certainly apply to money as well.

This is just silly. People in most of the world are able to build things just fine without using the American system of units.

Yeah just line it up with that non-existant mark on your measuring stick. Is it enough of a tolerance problem to really worry about? Likely not. But you still can't point to a specific line to measure too unless they have specially added 1/3 marks.

> you still can't point to a specific line to measure too unless they have specially added 1/3 marks.

You also can't point to a line to measure a quarter of an inch, unless they have specifically added 1/4 marks. What's your point?

I have a project where I need 3 wooden blocks, each perfect squares, to fit width wise in a 10” wide gap. I don’t want any space between these blocks sides of the gap they fit in. It’s an important project to me and I’m willing to pay a substantial sum of money.

But from what I am reading it sounds like you’re not able to do the job, the blocks need to be 3 1/3” wide each. It’s a no-go if I see someone try to cut them to 3 5/16”

What kind of system doesn’t let you cut such a fundamental length into thirds. Crazy.

I bet you that if I cut the blocks to 84.7 mm they would do just fine. If they don't, you take a file to one of them. And you have to do it like this with wood, anyway - because of imprecise saws, and moisture changes.

Yeah my point was every measurement system has some value you can’t easily divide into thirds. How you measure depends on your tolerances. I have no qualms using either system, but metric is a much better system in my opinion.

Counterpoint, the us already had undergone industrial revolution and had standardized size on inches. It would have been expensive to restandardize everything

I should add to the discussion somewhere that when I write code (or even do calculations) that deals with Imperial units, I just use the SI prefixes and end up with things like centifeet and kiloinches (miles are banished forever). It makes the code a lot easier and the people who are used to Imperial can tell what you're going on about.

Because adding 7/16ths of an inch to 7/8ths of a mile and getting an answer in inches isn't easy for a human. Adding 1cm to 982m and getting an answer in centimeters is dead easy for a human.

THAT'S why human intuition about measurement doesn't mean a damn thing.

Using metric means using the system optimized for humans. Period.

Your absolutism is a bit silly. I don't think the Imperial system is good for anything beyond construction or cooking, but there's a reason it excels those areas. And it's exactly because it's more usable by humans in certain contexts (like construction or cooking). 1/3 of a meter should not be an irrational number - how is that "optimized for humans"?

A scalable system that shares the divisibility of the foot would certainly trump both systems.

Nit: 1/3 of a meter is rational. You're looking for "whole number."

Correct - I've admittedly had a few beers.

Which might be obvious due to me debating the merits of the number 12 on the internet.

Well 12 is amazing, but arguably there are too many other negative aspects in the imperial system as a whole.

But 1/2 isn't a whole number either.

Base-10 absolutism rears its head again. The objection to 1/3 is that it has a non-terminating decimal expansion. This is not a problem if you're using base-anything-with-3-as-a-factor.

What about 1/5 instead? There's always going to be problems with some base, the point is that unit conversions are super easy with metric, and it's easier to teach to children.

As for temperature, 0 is really gold and 100 is really hot in pretty much every scale, that's just a very subjective way of describing things.

If you want to measure ⅓ metre, go ahead. Nothing stops you from doing that.

The usual convention in construction in Europe is multiples of 150mm, for example a typical large appliance is 595mm wide to fit a 600mm wide space.

The imperial system is not good for construction. Try measuring a 2x4 sometime.

It's just an established convention. And it sucks.

A 2x4 is cut to 2" by 4" wet and shrinks when it is dried. I'm no huge fan, but this is not an issue with the imperial system.

Uh, no. The final 2x4 product is milled mostly dry. Mills allow the timber to air dry, then mill, then post-kiln, and may mill the final product after that e.g. by cutting 2x4s out of a 12x4. The reduction of a 2x4 from 2x4" to 1.75x3.5" is done on purpose, because modern mills can put guarantees on the density of knots in the wood, thus requiring less wood for the same engineered strength guarantee. So the 2x4" product is not actually 2x4 because the mill is asserting that while there is less wood than just cutting a 2x4, the board they're selling is as strong as a 2x4 would have been at the turn of the 20th century, when they didn't have a way to guarantee the density of knots.

The imperial system is terrible for cooking, in my experience as a home cook and baker.

Measuring dry goods by volume instead of by weight? Good luck ever getting consistent results.

Base 10 math is the most intuitive for humans. Fractions are an abomination.

Math isn't intuitive for humans. It takes a lot of work to learn it and most people don't remember any of it past school age. If we taught base 12 instead of 10 it would be just as intuitive.

But we don't. The number system used in the western world is base 10. So why add base 12 on top of that?

It is appalling for cooking. Don't get me started on the shitshow of using "cups" to measure weight.

1/3 of a metre is 333mm, which is generally precise enough for construction.

How is the system good for cooking? Literally the first thing amazon echo was showcasing was unit conversions while cooking.

In what situation would you be adding 7/16ths of an inch to 7/8 of a mile? If you have such crazy tolerances you shouldn't be using fractions from the start. And even if you did, with imperial system you could just write '7/8 mile and 7/16th of an inch' or '7/8 mi. 7/16 " ' and when they measure it out they will measure 7/8 of a mile, then add on that 7/16 inch.

And whatever you are measuring that length with, fucking awesome job getting 1/16 or better tolerances over that amount of distance with .

Do people in metric-using countries commonly need to know what 982m + 1cm is? It never seems to come up here in the US...

Perhaps not, but nonetheless I instantly worked it out in my head without even trying.

These units are terrible for humans too.

Humans are good at base 10.

For this human, the relationships when (for instance) talking about water are great -

1g = 1ml = 1cm^3

Humans are naturally bad at base 10. This is noticeable when learning counting and arithmetic - children often skip 7 and jumble 6, 7, 8. Base-10 is not so bad once one has learned it, though.

Humans are really good at doubling and halving, which the Imperial system excels at.

That's false, the Imperial system is pretty bad at doubling or halving.

What's double of 3.7 feet? Or half of 1.5? What is 3.7 feet even? Is it 3 feet 7 inches or 3 feet plus 7th of a feet (This last question is a nitpick)

Any of these in metric are super simple, but just harder to do in base-12.

And I would add, it is not immediate to go from 200 inch to 18 feet 2 inches

In practice, as the previous poster pointed out, Imperial numbers are rational, not real. You wouldn’t normally experience ‘3.7’ feet.

Don’t get me wrong, I’m certainly not a proponent of the Imperial system (for instance, calculating prices for groceries is painful). I am just pointing out that the metric system doesn’t take into account many Human use cases (Base-10 isn’t great for Humans). It was a system forced upon people by an ‘ivory tower’, and consistent with US philosophy, it makes sense that they rejected it.

Americans are pretty awesome.

The imperial system is not even in a consistent base!

> They're more ... human, maybe

I think both systems of units typical cases are dominated by human factors. Anecdotally, humans tend to use one of three scales for their preferred choice of measurement and they tend to be smaller-than-human, human, larger-than-human.

For example, the km. I see mm, m and km used quite often.. but the other bases are almost never used. A prime case for this is "what is the distance to the sun?" If you're going to round your answer then the most concise form is 150 Gm, yet most people will still say something like "150 million km" which is unnecessarily long and non-canonical, but is much more familiar to the human mind and makes comparisons to everyday experiences much simpler.

You can see this factor occur with just about every other metric base unit, even though the conveniently prefixed part of the system would be "better" for all technical definitions. Just as easily you could use imperial units and just overlay the metric prefix and scaling rules on top of them and it would be no more or less accurate or better than the metric system of units.

> Use them all you like. I won't.

I use whatever is convenient or common for the application.. if it gets complicated or I need a conversion, I use a unit-system aware language or environment to do my calculations. It really obviates the importance of the choice of unit and allows you to think about the fundamental problem more clearly along with many other benefits including conversion of units at any stage of calculation.

Nitpick: centimeters are also used often.

> A prime case for this is "what is the distance to the sun?"

I was attending a kids planetarium show as a volunteer and the professor asked this question and a kid proudly shouted “1 AU!”

In Norway hectograms are frequently used. We use them for things like potato salad at the deli counter, pick'n mix candy, berries and small-time-dealer quantities of hash.

Imperial units are good for describing small items in 'feets' length, and for cooking measures.

I don't think miles have an advantage over kilometers.

In Canada, people have trouble understanding the various measures if '10ml' of this, or '10mg' of that.

They do understand 'a teaspoon' or a 'large spoon'.

I think we need some kind of colloquial measure for food.

Recipes in cups are one thing I cannot understand, I do have a scale, I can measure everything with that

"Recipes in cups are one thing I cannot understand"

You drink out of cups every day; this is what humans, even you understand.

'A scale' is inapplicable while you're buying food or reading labels.

Why use a scale when everyone knows what a cup and teaspoon are? They are human measurements.

But it doesn't matter what you use, what matters is what people understand, and they don't understand grams and millilitres.

It's been identified as a health problem: people don't have an intuition for the units on labels - there should be imperial units to help them understand.

As for litre/gallon or pound/kg I don't think it matters ... but consider for a moment that everyone in Canada that I know still uses pounds. And feet/inches for height.

I don't know a single person that can tell you their weight in Kg, maybe heir height in meters but they'd have to think about it.

My cupboard has cups in all kinds of sizes. Which one is the right one to use as a measurement? And for baking there's quite a big difference if my cups are 150 ml or 350 ml, especially when paired with counted ingredients like eggs. That's the problem with cups.

All of your regular coffee cups are exactly 250ml.

Regular people use them for basic baking all the time, like making pancakes.

'Cups' are still better measures than ml because even you, in your self-acclaimed ignorance have a sense of how much a cup is whereas people do not have any idea how much '300ml' is.

Canadians have no clue what 10ml of anything is.

Canadians will continue to use feet and pounds for personal measure, despite being surrounded by total metric system - that should tell you something.

Do you order beer in ml? Or pints?

Seriously, do you know anyone that orders a 473ml of beer?

So why pints? And not ml? Because it makes sense.

Everything should be in metric, but many things should also be Imperial because metric is not useful for many common measurements.

The entire construction industry in Canada still uses Imperial, and it also weirdly makes sense. Inches and feet are slightly more approachable at smaller scale.

How can you be sure that "all of your regular coffee cups are exactly 250ml"? And what about teaspoon? And everything else?

Everyone here is obviously biased toward his/her own measurement system based on our experience, but the fact that "3 cups and a half of milk" is more precise than "875mL of milk" is clearly false.

I didn't say anything about Imperial being more precise.

I'm saying it's often more useful.

1 cup mix, 1 cup milk + 1 egg.

1 pint of beer.

1 teaspoon of sugar.

These are things everyone can understand.

You can put the ml on the side of the label.

"That guy is 6 feet tall, about 180 lbs."

Is better than metric for most people.

"I'll have a glass of wine" instead of "I'll have 240 ml of wine"

Any one of you who orders beer by the 'ml' can keep arguing with me, but I suspect you all order 'pints' in which case you should consider for a moment why you do that.

> These are things everyone can understand

Eh, no, here in my country nobody uses that units, all the recipes and in the stores, the units are ml, kg, etc

> whereas people do not have any idea how much '300ml' is.

No, you get a sense of this if you live somewhere that uses ml for things.

One can of soda is 330 ml.

I live in Canada we use ml and nobody orders beer in ml.

5 grams of sugar? Nobody knows what that means.

They know what 5 tea-spoons is though.

I'll be $100 that if they put 'teaspoons of sugar' instead of grams, people would be shocked. There are videos showing how much sugar in a can of Coke, and it's largely because people are oblivious to the units on the label, which we can all technically read.

For 300 ml there are measuring cups that have a scale on the side. Same for 250 ml by the way. Incidentally, I wouldn't be sure I could actually measure 1⅕ cups of anything (under your assumption that a cup is exactly 250 ml (Do I fill them completely? One cm below the top? And while about 50 % of the cups here seem to roughly fit that size, the others are different.)).

I don't order beer at all, but around here it's usually ordered as 500 ml (a little further south, especially around October, they tend to order 1 liter).

And here I thought 1 Imperial cup was ~284 ml... 1 US cup is closer at 240 ml. Might get away with that discrepancy when cooking, but when baking, not so much.

Especially if you're using things like flour where you get different quantities which if you sift it, or spoon it into the cup, or scoop it from the bag.

Cups are fine for rough and ready, but terrible for baking.

For mass, distance, area, and volume metric has an obvious advantage because for all of those we regularly deal with such a range of values that we want subunits, and basing those subunits on powers of 10 fits in much better with our number system and makes computation and conversion easier.

This lets one make a pretty good argument that metric has advantages sufficient to justify having to buy new rulers and scales.

For temperature, what is the justification for switching from F to C? We don't usually subdivide temperature units, so really all C does different from F is change the size of the degree and what physical process the scale is calibrated to.

One can argue that the physical processes chosen for C calibration are more convenient than those for F. C was 0 == water freezing, 100 == water boiling. F was 0 == temperature of a mixture of water, ice, and ammonium chloride, 100 == body temperature of a healthy man.

But that could have been fixed without changing the scale at all. Just redefine F so that 32 == freezing of water, 212 == boiling of water. That would fix the one problem F had without requiring anyone to get a new thermometer.

> what is the justification for switching from F to C?

The rest of the world already using ℃. Imagine no more dual scale thermometers, no more switches in weather apps, etc :D

Sorry, I guess I was not clear. I didn't mean what would be the justification for switching from F to C now in the US.

I meant what was the justification for adopting C initially for the metric system instead of using F?

For other metric units, there were serious problems with the pre-metric units. For example, Wikipedia says that by the time of the French Revolution, the existing system had become impractical for trade.

It doesn't say why it had become impractical, but my guess would be it had a lot to do with no good standard values for the units. If the units are not well defined in a way that gives the same values everywhere, it makes long distance trade harder.

I base this guess on doing some research once to figure out why they did not defined the meter to make conversion to Imperial easier. Since they were free to define the meter any way they wanted, they could have made 1 meter == 1 yard, which would have made conversions of long distances easier. Or they could have defined the millimeter as 1/25th of an inch, which would have made conversions of short distances easier than the 1/25.4th of an inch that we ended up with.

As far as I was able to determine, this was never an option because, as far as I could find, there was no widespread agreed definition of inches, feet, yards, etc. All that was standard was the relationships among them (1 foot == 12 inches, 3 feet == 1 yard, and so on).

There probably was no way to fix that without adopting a completely new unit, because if they tried to just make a new standard for, say, the yard I'm sure it would have gotten bogged down in arguing over whose yard to base it on. The French would think everyone should adopt their yard, the English would think everyone should adopt theirs, and so on.

So, a new unit, based on something not tied to any one region or nation, makes sense.

Temperature did not suffer from this, or did not suffer from it in a way that was not easily fixable. F was based on a reproducible physical 0 point based on the temperature of a brine with a self-stabilizing temperature. The only problem F had was that there had been some waffling over the other calibration point, which had been fixed well before the first attempts at a metric system.

So...why did they pick C?

Fractional units are extremely useful in construction and machining. Now you could use fractions with meters, but nobody does, and im not sure why other than 10 is a shitty starting point for fractions and you end up with crazy fucked denominators.

The typical woodworker knows by hard all “crazy fucked” denominators like 333.333 mm for a third, 200 mm for a fifth etc.

The idea that not having straight fractional values somehow makes it harder is just plainly false. When you tell anybody to cut a third of a meter they will just happily cut 333.33 mm down to their usual tolerance

For most things, I think metric makes more sense, but I fully agree about temperatures. Fahrenheit is a superior scale for humans.

Co-signed! The freezing and boiling points of water are also not particularly pragmatic points of reference. I don't think "I need to lower this to 0°", I think "I need to put this in the freezer".

> The freezing and boiling points of water are also not particularly pragmatic points of reference.

I must strongly disagree.

The freezing point of water is an incredibly important and pragmatic point of reference for hundreds of millions of people around the world, who live in places where water can freeze (or thaw) on its own outdoors. Not just for transportation, but also its affect on biology in agriculture.

While the boiling point is (thankfully) not important for weather-reports... Cooking! What would you do if I said to "simmer" something? You aren't supposed to go high enough to reach the obvious boiling point, so how are you supposed to know when you're close enough if you can't remember the magic number?

I'll concede that freezing is very important to a lot of people, but at the same time, I don't think it's particularly onerous to remember that the freezing point is 32 degrees.

As far as boiling and cooking, I would argue that there is no magic number anyways, since boiling point is variable by elevation. At 7500 feet / ~2250 meters, water boils at 198°F.

> As far as boiling and cooking, I would argue that there is no magic number anyways, since boiling point is variable by elevation. At 7500 feet / ~2250 meters, water boils at 198°F.

That's an excellent point, let's examine the relationship between altitude and boiling point, in both American units and everywhere-else-in-the-world units [0]:

5000 feet -> 202.97 F

7500 feet -> 198.33

10000 feet -> 193.6 F

Compared to:

1000 meters -> 96.73 C

2000 meters -> 93.38 C

3000 meters -> 89.95 C

In both cases, the boiling points at altitude are magic numbers. The difference is that with Celsius, you can interpret degrees as "percentage of the way from freezing to boiling". Going from 100 C at 0 meters to 90 C at 3000 meters is immediately meaningful as a 10% decrease. With degrees Fahrenheit, that same 10% drop in boiling temperature that happens at around 3000 meters / 10,000 feet is 212 F to 194 F.

0: https://www.omnicalculator.com/chemistry/boiling-point-altit...

Excellent point.

100 -> 90 is 10% decrease.

212 -> 194 is ~8.5% decrease (and I had to go out of my way to count that).

Also: Celsius converts easier to Kelvin which is sometimes useful

If going from 100 °C to 90 °C was a 10% decrease, then going from 0 °C to 1 °C would be an ∞% increase. Metric units are superior to imperial for many reasons, but this isn’t one of them.

Good thing Fahrenheit's got pragmatic points of reference, like. . . the freezing point of brine water and almost the body temperature of human [1].

[1]: https://en.wikipedia.org/wiki/Fahrenheit#History

While having a "wider spread" of "today's forecast" numbers is nice, that 32-degree offset is a huge negative ding against it.

I mean, there's a big important point where you start getting solid things falling on your head and slick icy roads and ruined fruit-plants, so it ought to be at more meaningful spot, like 0.

I can just barely feel the difference of temperature of one degree Celsius. I really don't feel multiplying that by 1.8 will make a big difference in how good a scale it is for humans.

As an example, the common temperatures in NYC range from 0-100F. In celcius that's like -18 to +38.

I'm a scientist and an engineer, and in those applications C is often better. But in daily life, Fahrenheit makes a ton of sense.

If you live in NYC, maybe. A lot of people don't, and you can find places where ranges in C are "neater" than in F.

> If you live in NYC, maybe. A lot of people don't

Those people are free to use whatever units they like. It doesn't have much bearing on the point that Fahrenheit, which is used in the United States, is a good match for the climate of most of the United States.

Most of the United States doesn't have climate that falls within 0..100 F. There are plenty of places that are more like 30..90 F etc. And I don't see how that's any different from, say, 0..30 C.

OTOH, as far as weather goes, C has the nice property that anything below zero is freezing temperature. In any locale where snow and ice is a thing, that's handy to know.

In Ecuador the temperature ranges from ~60 to ~90F, but I'm sure for them is a great relief to know people of New York have a temperature unit that perfectly matches their climate as neatly as going from 0 to 100.

But is 15C to 32C better?

Just think about it by 10s, as you do with the metric system:

20 C - a bit less than room temperature (68 F)

30 C - pretty hot (86 F)

40 C - very hot (104 F)

And going the other way:

10 C - a bit chilly (50 F)

0 C - cold (32 F)

-10 C - real cold (14 F)

-20 C - really really cold (-4 F)

When you hear a temperature in Celsius, don't try to convert it to Fahrenheit, just think in Celsius. 15 degrees is halfway between "chilly" 10 C and "room temp" 20 C. One degree of warming - say 26 C to 27 C - is pretty easy to conceptualize when you have those 10-degree reference points.

This is the right answer for Americans. The reason I prefer Fahrenheit is because it is the one I know what degrees feel like and because Celsius isn’t reported in enough resolution.

If it was always reported to the half point I think we would be able to relate to Celsius better. And if I was making a population wide change I’d ensure reporting was always to the half degree.

We just report it to the degree (high of 34 tomorrow, 32 the next day). That's really plenty of resolution for non-scientific measurement.

And is also more resolution than the error warrants

I think I meant less for forecasts and more for weather apps and thermostats. I really think it could help with adoption. But if it’s not warranted by the error then maybe I’ll reconsider.

The precision on most digital thermometers for home use is (surprice) +-1 degree C :-)

When it is 0 C, you can expect ice/snow outside.

Yesterday it was +20 C, today it is +25 C, so it is noticeably warmer.

-10 C tomorrow, so you'll need your woolen cap and padded jacket. -20 C and add a layer of underwear underneath and maybe a scarf.

When you boil water for tea (100 C) and don't want the water boiling but still hot, aim for 95 C.

When the inner temperature of salmon is +46 C, it is perfect, if it is +56 C or more, it is thoroughly cooked and will not taste soft anymore.

Usually the relevant difference is 5 or 10 degrees.

I don't even want to think what those examples could be as Fahrenheit.

My point is it is eventually a matter of what you are used to, but Celsius is more logical, because it is directly tied to water freezing and boiling.

For the most logical measurements we'd use Kelvin, but it is not practical! "Oh, it is 273.15 K outside, might be black ice on the roads"

I hadn't thought of some of these advantages. Some are subjective, but it's hard to deny the intuitive nature of others. I say bring back the span and the rod as well.

Go walk a job site with a tradesman and youll see why imperial is so useful and natural to them. They walk off long distancrs, use knuckles for small ones and do complex division with ease.

Because they have to since they're stuck using imperial. The imperial system does not make people better, it forces people to use fractions.

My father lays tiles for a living and he always did the same in metric, if he didn’t had something to measure things with him (which any professional should!)

A meter is basically a slightly longer step. I think most tradesmen over here got a pretty good sense how to walk a meter.

0.1m or 1dm or 10cm or 100mm is basically the width of your hand.

1cm or 10mm is roundabout the width of the pinky finger

I feel like imperial units are human units. they are units used on a human scale, where as metric are more 'computer'. example: a human really cant look at something and divide it by 10 very well, but 1/3, 1/2, 1/4, very easy to do. the sizes makes human sense, like a foot being about a human foot, etc.

But they're not! My foot is 25cm, far from '1 foot'. My thumb is 1.5 cm wide, far from an inch. The metric system is actually much more human for me. And I never needed to measure 1/3rds to 0.02mm precision without a precise measurement instrument. And if exact precision doesn't matter then all these arguments about fractions are moot, too!

considering your foot is 2 standard deviations from the mean foot length, that hardly proves anything

Well it proves a lot in my opinion. Feet are really non uniform in length by a lot.

go to google and type "about definition"

You can't both say that meter isn't exact enough when meassuring 1/3 and also say that 25 mm wrong on a food is ok...

I didnt say exact, just not easily done aka intuitive. a concept probably lost on you ages ago

I don't get that one. It might be just that you are used to it.

A meter is a slightly longish step.

A decimeter is the width of a hand.

A centimeter is the width of a pinky finger.

A milimeter is twice the thickness of your fingernail.

It is actually no less or more intuitive than the imperial system (except when it comes to calculations, unit conversion and interfacing with other SI units like Volts, Joules, Watts etc.) I feel very comfortable working with digits like 12.5 or 33.33. I think a lot of the imperial-versus-metric-debate boils down to the question how big your love for fractions is and how things are measured around you. If everything is built with 2 by 4 wood, then a metric system is inconvinient. If your hardware store sells 4x8cm wood, then going to inches would be inconvinient.

Most probably because you grew up with it. I’m pretty sure you think the same about your religion, nation, race ... but be sure eveybody else in the world may think the same of their own. And they’d be right too.

What I personally find disturbing is how irrational positions such as yours are commonly accepted in a supposedly advanced society. It leads to a pretty bumpy road, time and time again.

There isn't anything more rational about demanding base 10 systems.

Last time I checked base 10 was quite common for pretty much everything but the imperial system.

Well I actually grew up with the metric system. I'm also not the religion I was raised. I do love my nation, which is easy because I'm American and there is a lot to love.

Imperial units are just better for humans to use. I would love if somebody could give me a redeeming quality for metric, but so far nobody has.

It’s easy to convert between units, miles and yard and feet and inches make my brain have a BSOD

One reason to avoid imperial units is that people seem to be generally unsure if they're even using them! I might be wrong, but you're probably more familiar with the US system rather than imperial units (given you said you're american). Did you know there are 20 fluid ounces in a pint?

I generally find them easier to manipulate, which is a frequent use for measuring distance. Honestly, I think the big thing hampering metric adoption is that no one uses decimeters. Kilometers are useful for trip distances, centimeters/millimeters are useful for small/precise measurements, but meters are deeply unuseful (for the same reasons you rarely see things measured in yards).

1/10th of a meter gets you a lot of the same usability as a foot measurement, but now adding centimeters onto that is more straightforward. A lot easier to calculate for measuring space for furniture, height, etc. . .

We do actually work in decimeters a lot, we just refer to them in 10cm increments. And conveniently there are 10 units of 10cm in a meter.

That’s usually called the zeal of the convert. First generation immigrants are quite adept at it.

As a proponent of the metric system, I got to say the most disturbing thing is how an honest because openly subjective, intelligible and relatable statement (like the one OP gave) can be turned into something political and offensive. It it is the habit of doing this, that leads to a bumpy road ahead.

But since we‘re talking politics: it were the „progressive“ Bauhaus proponents like Corbusier, that proclaimed that what we build should use human scale as foundation of measurement. What OP said is exactly that.

It’s neither intelligent (as in based in some objective rationale) but subjective and capricious. It’s not relatable unless you’re also into the imperial system. And I’m not talking about politics: you will find the same people everywhere.

But I also find unlikely you support the metric system, at least other than for white knighting random strangers that you happen to agree with.

On top of that I don’t see how imperial is more human than metric. Yeah you have the foot bit a meter is a slighly longish step. Both units make you walk weirdly.

And what I personally find disturbing is your idea that their view conflicting with yours is somehow an indication that they are obstructing advancement. To me, that seems much more problematic than them favoring the number 12 for common measurements.

Weasel words. I could easily justify pretty much any barbaric idea in the same terms, and it’ll fly among a certain subset of US citizens. Which honestly is worrisome to say the least, regardless of you agreeing with such idea.

> irrational positions such as yours

This is, frankly, insulting. You may disagree about the merits of blhack's arguments, but that doesn't make them illogical or unreasonable.

It would be one thing if you said, "Here's why I think blhack has got it wrong, and why the arguments presented don't hold water." But you just tossed an insult without bothering to refute. Bad form.

I see you're not liking how many feet are in a mile (and many other silly things).

Well I also don't particularly care about how many feet are in a kilometer, since they are different units.

A mile is...a mile. A half a mile, a quarter of a mile, an eighth of a mile, etc. Yeah, there are 5280 feet in a mile. There are also 25.8 or something like that mm in a inch, some other arbitrary unit of conversion that we all have to memorize.

Your second example is disingenuous. Mm to inch is going to be a weird conversion because they are between different unit systems. Feet to miles is unacceptable considering they're both imperial units.

These differences get important if you do any type calculation in engineering or physics.

Then it suddenly starts to matter if the result is Nm, Nmn or a Newton times a inch

Example: a Volt – which also the US uses with its metric prefixes – is defined as a Joule or a Wattsecond or a Newtonmeter.

No matter what is suggested, no matter how much better the alternative, there will always be a group of contrary people. Look at flat earthers. Look at anti-vaxers.

There are actual benefits to some imperial units when working in small amounts. They can often be subdivided much more easily into amounts that are harder to handle (or at least require going to another order of magnitude to do accurately).

For example, dividing a foot into thirds or fourths is trivial, but for a meter it requires either going two orders of magnitude (25/100ths for a quarter) or simply cannot perfectly represent the amount (1/3).

Now, not all imperial units have sane definitions, and they don't even all follow similar rules (8 fluid oz. to a cup, 16 fluid ozz to a pint, you lose thirds but can still easily do fourths).

In a lot of ways, base 10 is really substandard to base 12, we just used base 10 because it's physically easy and socially ingrained. Who knows, maybe 100 years from now we'll teach in base 12 and have a new system that's base 12, and all the metric die-hards will been seen as backwards yokels that cling to a clearly substandard system because of history and it's what they know? I mean, I really, really doubt it, but it would be better than the metric system as long as most people could easily think in base 12 (which would require a massive social upheaval).

"It cannot perfectly represent the amount" you say, and then perfectly represent the amount.

You represent a quarter as the fraction 25/100ths to show how impractical it is, instead of writing 1/4.

Would it be so hard to build a ruler with thirds measured on it, so you don't need to try and guess 0.333333 from mm readings? Like http://teaching.monster.com/nfs/teaching/attachment_images/0... but made of metal

> "It cannot perfectly represent the amount" you say, and then perfectly represent the amount.

Actually, I said "It cannot perfectly represent the amount (1/3)", so I specifically game an example immediately after the statement of exactly what I was talking about, which you then ignored and used an example for a different item to represent erroneously. What's up with that?

> You represent a quarter as the fraction 25/100ths to show how impractical it is, instead of writing 1/4.

No, I represent a quarter as 25/100's to show how it would be accurately represented in metric. 1/4 meter is not pure metric, it's applying a non-metric modifuer to a metric amount. The metric representation of 1/4 meters is 25 centimeters, which is 25/100.

Let me lay it out side by side:

- 1 and 1/2 units Imperial: 1 foot 6 inches or 18 inches Metric: 1 meter 50 centimeters or 15 decimeters or 150 centimeters

- 1 and 1/3 units Imperial: 1 foot four inches or 16 inches Metric: 1 meter 33 centimetersa and 3 millimeters and... or 133.33... centimeters

- 1 and 1/4 units Imperial: 1 foot 3 inches or 15 inches. Metric: 1 meter 25 centimeters or 125 centimeters

That's not to say imperial units are good. They are hard to use for most things because they change across types of things measures, and counting in twelfths when needed is much more painful than in tenths.

But, if we were taught in a 12 base system we would be able to use it easily, and base 12 has more cases where it can be used easily than base 10. Everything else would be the same except than our sense of scale would be a little different and we would have an easier tome subdividing things in many cases.

Metric isn't an optimal system, it's just the optimal system for right now and the world we currently live in. But for a few historical turns of fate, it might have been very different.

> Would it be so hard to build a ruler with thirds measured on it, so you don't need to try and guess 0.333333 from mm readings? Like http://teaching.monster.com/nfs/teaching/attachment_images/0.... but made of metal

Then it's not metric. That's the point. We use these values anyway, yet you have to step outside the metric system to represent them easily. Adding extra marks that don't correspond to the regular intervals is confusing, so it's avoided. That's why most rulers in the united states show metric on one side and imperial on the other.[1]

1: http://cdn.dickblick.com/items/554/27/55427-1012-3ww-l.jpg

>No, I represent a quarter as 25/100's to show how it would be accurately represented in metric. 1/4 meter is not pure metric, it's applying a non-metric modifuer to a metric amount. The metric representation of 1/4 meters is 25 centimeters, which is 25/100.

What? Fractions aren't exclusive to the imperial system.

1/4 of a metre is metric, just as a 1/4 of an inch is imperial.

Everything below is a perfectly legitimate way of writing metric units:

1/4 m = 6/24 m = 3/12 m = 0.25 m = 25 cm = 250 mm

So easy!

Fractions are mathematical modifiers that can applied to any quantifiable measurement. That said, I imagine they aren't generally used in professional context in metric, because they generally aren't in imperial either. You don't see architectural plans that say 1-1/2 feet, they say 1'-6". Is it common to see fractional amounts in metric when used in a professional context?

Usually we write everything in mm for professional context.

Thanks, that's what I assumed (because it makes sense). For metric you often go two orders of magnitude smaller, but I'm thinking a good amount of the reason to usually go straight to millimeters instead of also using decimeters is that decimeters just can't easily represent many common fractions of a meter (1/4, 3/4, 1/3, 2/3), and a base 10 system can never represent some of those perfectly without resorting to a mixed format.

Buy an imperial rule.

There's some inches that are sub-divided into tenths (maybe 1/20), and others sub-divided into sixteenths (maybe 32nds or 64ths). Often with heavier markings on more significance. For easy division and fractioning of whatever it is you are doing.

If it's imperial only (v. rare nowadays) there's usually a coarser scale or two for easier subdivision or when the 16ths and finer just don't matter.

Buy a metric rule.

There's mm, cm, and metres. Nowt else, not even weighting of marks except usually 1cm or 5mm. For measurement this is fine. For division such as in woodwork, metalwork and building, this is often a pain in the ass.

Metric only usually engraves just one side or exactly duplicates. No coarser scales.

So even when working in metric I often find an older imperial rule a better working tool(!)

How often is the distance you need to divide a whole number of inches anyway?

No more often than it is a multiple of 12mm, 60mm, or whatever.

Real distances are either designed for easy calculation, like my N*150mm kitchen pieces, or are some random length.

As someone who does a lot of woodworking in a metric world: the common fractions (e.g. 1/3) are not a problem at all, they are periodic. Adjusting my saw to 333.33mm or 6.66mm is something I do quite often.

If you use fractions often or work with weirder fractions anybody who is worth their grain of salt will build custom temporary rulers or helper systems anyways. And then it won't matter at all if your unit is hyperinches or fractions of lightspeed traveling through frozen beer in a second.

I can see how anybody who grew up with inches likes that one better, but in the end it is just numbers on a scale.

> If you use fractions often or work with weirder fractions anybody who is worth their grain of salt will build custom temporary rulers or helper systems anyways.

My point is a system with less need for that because it can handle more common divisions easily would be good.

> I can see how anybody who grew up with inches likes that one better

I tried to be very explicit in that I was not promoting the imperial system. I'm not even promoting imperial distance over metric distance. I'm purely using feet because there's a base 13 for inches to illustrate how a full base 12 system might work. Feet and inches are much worse than metric even in this case because that conversion only happens at one spot, not at regular orders of magnitude.

All I was saying is that since it's a fact there are some things that can be done in base 12 that can't be done in base 10 but not the other way aroubd, it would be really interesting (and extremely unlikely) if we somehow shifted to a base 12 metric-like system. That wouldn't be imperial (which has a different conversion every time you blink).

I learned a lesson though. People are very protective of the metric system. Even opining about fictional future possibilities with mathematical facts will lead to downvoting into oblivion and people misinterpreting clear assertions as something they aren't.

> My point is a system with less need for that because it can handle more common divisions easily would be good.

My point was, that from a practicle standpoint this doesn't really matter. If you need to tick of a third of a meter somewhere just a few times, everybody would just happily make a mark at 333.33mm – if you need to do this 50 times, building a temporary ruler is a good idea in any measurment system, because it reduces both cognitive load and the likelyhood of mismeasurement. This is especially true if you are building something that involves many steps that are repetitive, similar, but different enough to ruin your day if you fuck up.

For me one of the best things about the metric system is, that it in fact is base10 because it eases the conversion and calculation between units and has cool effects that imo outwheigh the cool things you would get from going base12.

Going base12 in a good way would mean going base12 fully, including temperatures, currencies, voltages, weight, etc. and this would mean turning a whole culture of knowledge upside down and inside out. If we would have a world dictator they might try something like this. From a distribution perspective it is desirable to have one standardized unit system that makes sense.

So my pain point isn't exactly metric vs imperial, but that in 2018 we still need to deal with these two systems and the conversion between them. Metric is far more wide spread than imperial and this has reasons, some historical, some political, some practical. If you are one who thinks national unilateralisms are a waste of energy and potential, you are certainly in favour of the metric system, just because it would be easier for the world to agree on going fully metric, than it would be for the world to go fully imperial.

And I am not talking about everybody having to use it in their day to day life – just look at the UK. I am talking about certain space agencies, industry, electrical engineering etc, where these things can have real graspable consequences, maybe even deaths.

That's actually my point. Whilst I use metric for almost all things, an imperial rule is, for me, a better temporary custom rule for actually doing stuff like centre finding or sub-dividing, than the metric ones. The units don't matter a jot, the markings and spacings do.

Which is why I keep one of each in the tool chest. :)

> but for a meter it requires either going two orders of magnitude (25/100ths for a quarter) or simply cannot perfectly represent the amount (1/3).

What? you switch to metric and suddenly fractions are not a thing any more?

1/3 m is just that, one third of a meter, perfectly. How is that so complicated? It can also be 333.3mm. And no one would write it as 333/1000 to make it seem more complicated than it is.

That's... not the same thing. One is: system that is mostly always better but can sometimes be handy for certain contexts. The other is: objectively true thing versus objectively false thing.

I understand some of what you say, but the point of standard unit is not so that people can choose which unit they like. It's to make sure everyone uses the same ones. If all but a few countries used imperial as their standard measure then I'd go for it. But right now it's the odd one out. Itu mostly survived only thanks to being associated with an economic superpower, so international companies can't afford to ignore it.

Hate to break it to you, but international companies do ignore it unless they need to print something out for an American to read.

Yes, but I suspect they bother to print anything at all is because the US is a big market. Unfortunately, this helps perpetuate those legacy units.

While I agree that in many ways imperial is better than metric in the way that you mention. It is absolutely atrocious when it comes to weight and volume. A gallon is still a base 10 unit of measure of water (10 pounds of water). Then only after that, is it in base 8 rather than maintaining that base 12 consistency.

Then if you look at imperial units of weight, it deviates away from base 12 again. It counts upwards from a pound using base 14 with stone and ton. And then when counting downwards it uses base 16 for a little bit with ounces, followed by out of nowhere throwing in a 1/7000 for a grain unit.

Even ignoring the scientific applications, none of this is easier for visualization purposes than grams or kilograms, nor is it all that useful for volumetric units either with maybe the exception of using cups instead of milliliters for cooking.

>> "A gallon is still a base 10 unit of measure of water (10 pounds of water)."

Not sure what you are getting at here. A gallon is about 8.3 lbs (3.8kg).

A gallon is 128 oz, a nice base-2 number.

You are arguing the difference between an imperial gallon and a US gallon.

Further evidence of how stupid these measurements are.

A gallon is NOT 10 pounds of water.

Rough conversions: 1.1, 2.2, 3.3 for volume (quart to L), weight (pound to kg), length (foot to m).

One gallon is: 4 quarts * (1 L / 1.1 quarts) * (1 kg / L) * (2.2 pounds / kg) = 4 * 2.2 / 1.1, so a gallon is roughly 8 pounds.

It's true that (for example) a third of a metre isn't expressible accurately in decimetres, but you can always just say (continuing this specific example) "a third of a metre". Nobody will be confused about what you mean.

This is however perhaps a good argument in favour of non-decimal currency.

It doesn’t matter. Just write 333.333 mm and if you make it evident in your construction drawing that three of these third meter-things need to fit one meter somebody might even calculate the width of the blade into it.

Measurements are just a number and you will always have tolerances and chains of measurements to go with them to clarify what you expext as a end result.

Yes, good point - I was thinking about casual, everyday uses, but if you're going to be precise then the question of divisibility becames even less relevant. Just tack on as many decimal places as you need.

It's true that this applies just as much to non-metric units, of course! But then if divisibility isn't a big deal, this goes both ways - meaning that the disadvantages of the metric system's base 10 orientation may well be minor in practice, and not enough to outweigh the advantages.

(Actually though I think the metric system has you more cleanly covered for this sort of case, with its consistent set of prefixes for scaling up and down by 1,000. Non-metric units tend to be a random jumble of 8s, 12s, 16s, or worse.)

Next you'll be promoting "a better way to count" by Conlang Critic Jan Misali - https://www.youtube.com/watch?v=qID2B4MK7Y0

Divisibility by 12 could have benefits when working with small numbers, but on the other hand multiplying by 12 doesnt sound like operation you can do easily from top of your head...

Presumably, you'd also adopt a base 12 number system, so that decimal 12 becomes 10, and decimal 36 becomes 30, etc.

Good luck with that

Hmm, good for usage you say. Ok, let's stick to "standard" imperial units. How many feet in a yard? Yards in a mile? What the hell is a quart? And since base 12 is great, what is 12 feet called? 144 feet? A 12th of an inch?

Or, ounces: How many ounces in a gallon? A pound? And how many _kinds_ of ounces are there, anyways?

Fun fact: The term “ounce” is of Latin origin from the word “uncia” which means “a twelfth part.” http://www.differencebetween.net/science/mathematics-statist... So...what's an ounce a twelfth of?

Or, say, a pint. What's the definition of a pint?

A pint is what British people drink in pubs while chastising the US for not adopting the metric system.

And then complain about gaining a stone?

The metric pint?

When they pour 500 mL into your 1 pint (473 mL) glass.

568ml, as god intended. Not some 450ml abomination!

We don't really use pints for measuring anything else these days.

If only US pints were a 450ml abomination.

That's about 50ml more than I'm used to getting when I order a "pint".

You are benefitting from the true Imperial pint where there is 4546 mL per gallon.

And of course 4 quarts to the gallon and two pints to the quart.

Otherwise like in the US in what is commonly known as the English system there is only 3785 mL to the gallon.

> So...what's an ounce a twelfth of?

It's a twelfth of a troy pound, or Roman libra (lb).

These two episodes from The History of English podcast trace these seemingly arbitrary units through history and give them some context. My favorite is the derivation of 5280 feet per mile. Also, that "mark twain" is a depth sounding of two fathoms.

http://historyofenglishpodcast.com/2018/07/26/episode-114-th... http://historyofenglishpodcast.com/2018/08/21/episode-115-th...

A yard is three feet, or about the length of a man's stride.

A quart is about the maximum amount of whiskey one can drink without dying.

A pint's a pound, the world around.

My favorite is the cord, which is 128 cubic feet, or more often a stack of firewood 4 feet tall by four feet wide by eight feet long.

A yard is not just a measure of length, but of volume and in a manner, constitution if you will, as it is also 2 1/2 pints[1], good sir or ma'am. Oy!

1. https://en.wikipedia.org/wiki/Yard_of_ale

Between that and the GP, we could establish a conversion between yards and quarts.

A pint is a pound so long as you're in the US. Everywhere else, it's 20 fl.oz, while a pound is 16 oz.

The cord is also the size of the standard US pickup truck bed with the wood stacked up about cab height.

0 degrees Farenheit is also the temperature salt stops freezing water. It is a good thing to remember when you are wondering about driving on snowy and icy roads.

Base 12 is more convenient than base 10. But that argument really only works if numbers were written in base 12. They're not, though, and that isn't changing any time soon. As a result, Imperial has to deal with two bases - the units themselves are defined base 12 (more or less; it's not really consistent e.g. with volume), but then you still have to do arithmetic in base 10.

So, until such time as we switch to base 12 for all numbers, metric is superior, because it is simpler.

You're right - imperial is far superior for precise building or manufacturing work.

Take drill bits, for example. Obviously it's much easier to figure out that 11/32" is less than 3/8". Or is it more? No, I'm pretty sure I was right the first time. The metric ones with their 5.5mm, 6mm, 6.5mm sequencing are just too complicated to work with, in comparison. And half a millimeter isn't very precise - it's much bigger than 1/64". Well, a bit bigger. Let's not get into tenths of millimeters.

And at larger scales, of course, base 12 is much easier when it comes to dividing distances. Taking a distance of 2'7" and dividing it by three in your head is much easier than dividing 79cm by three, because... well, 2' divided by three is 8", obviously. If you need to be sure, just tap it into a calculator. That supports base 12...

Anyway, you'll quickly determine that it's 10 1/3", which is much more precise than 26.3333cm. Now I just need to subtract the radii of these two 5/16" holes from that, which is easy - imagine trying to subtract 8mm from 26.3333cm! What folly.

Whether decimals or fractions are used is not necessarily related to metric vs. customary units.

I just weighed myself on my bathroom scale -- 191.2 pounds.

People use "stones" for weight of humans. As if 14 pounds is a convenient amount.

These are problems you actually pretty much never have in actual precision manufacturing in metric... Most general machining is done to a tolerance of +/- 0.1 - what does half a millimetre have to do with anything?

As for building, that's mostly just rounded to the millimetre, centimetres aren't usually ever used.

The gp was being sarcastic.

Do I detect sarcasm here? I'm pretty sure I detect sarcasm here.

Much of the sarcasm targets the mixing of multiple units that is everpresent in imperial measurements. Feet + inches instead of one or the other?

I detect 1.23 furlongs of sarcasm.

I understand, that you know the metric system, and, judging by your reasoning for your love for the imperial system, I understand, that you know what you are talking about (better than me). So, please, do not understand my comment as wanting to advise you! It's just, that I found this (on the web, one day) to express so much the way I (having grown up with the metric system) feel about it:

"In metric, one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade -- which is 1 percent of the difference between its freezing point and its boiling point. An amount of hydrogen weighing the same amount has exactly one mole of atoms in it. Whereas in the American system, the answer to 'How much energy does it take to boil a room-temperature gallon of water?' is 'Go fuck yourself', because you can't directly relate any of those quantities."

From: "Wild Thing" by [Josh Bazell](https://en.wikipedia.org/wiki/Josh_Bazell).

Actually, assuming room temperature is 60° and you’re at sea level, it’d take 1,216 BTUs to bring a gallon of water to a boil. A BTU is the amount of heat (which is energy) required to heat one pound of water one Fahrenheit degree; a pound of water is a pint; there are 8 pints in a gallon (2 pints in a quart, 2 quarts in a pottle, 2 pottles in a gallon). So, 8 * (212-60) = 1,216.

1 US liquid pint is defined as the volume of 1.041 lb of water at 62F. The British imperial system is a bit cleaner where 1 imperial pint is defined as 20 oz or 1.25 lbs, at 62F.

"A pint's a pound the world around." I never knew whether that came from the fact that both are 16 ounces or because a pint of water weighs a pound (approximately). I prefer to think it's the latter. Makes it so I can remember that a gallon of water is approximately 8 pounds. 5 gallon pail mostly full, probably 35 pounds. Nice.

Except it's not, as a pint is 20 fl.oz, while a pound is only 16 oz.

UK resident here, in case you couldn't tell :).

I suspect that only a minority of people in metric-using countries -- those with basic chemistry knowledge fresh in their mind -- know that "one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade".

Probably a similar number of Americans know the same facts. And any of them would answer "How much energy does it take to boil a room-temperature gallon of water" in the only sensible way -- look up the conversion of gallons to liters, do the calculation in metric, and convert back from calories to whatever unit you want (BTUs, I guess).

The point is: nobody, including Americans, uses the customary system in chemistry labs. Nobody ever has cause to calculate how many BTUs it takes to boil a gallon of water without reference to the metric system. So the argument is a bit specious.

>I suspect that only a minority of people in metric-using countries -- those with basic chemistry knowledge fresh in their mind -- know that "one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade".

I wouldn’t be so certain about that. I’ve used that to conceptualize volumes and weights ever since I first learned that in school.

You comment on HN threads about measurement systems. You are not normal. None of us here are.

Nice point, but it is really the typical elementary school topic "one cubic centimeter of water is one gram, one cubic decimeter is one kilograms, one cubic meter is one THOUSAND!!! kilograms" Then in highschool it is used for physics and unit of measurements and everyone knows that you can just weight milk and water when you cook with 1kg = 1liter

Normal people don’t do that. They just know that a gallon is a gallon, a meter is a meter, a pound is a pound, etc. People rarely have need to convert between mass and volume. And they don’t weigh their milk or water.

Because if they had to, they'd rather find a jug than a calculator.

Also most people (in the US at least) do not have kitchen scales!

> I suspect that only a minority of people in metric-using countries -- those with basic chemistry knowledge fresh in their mind -- know that

This is not the case. This part: "one milliliter of water occupies one cubic centimeter, weighs one gram" is known by most people, even kids in primary school. In other words everyone knows that a litre of water weighs one kilogram, and that there are 1000 litres in a square metre. I concede, though, that at least in Italy, which is the country where I was born and raised, most people wouldn't know the next part: "and requires one calorie of energy to heat up by one degree centigrade".

"Everyone knows there are 1000 litres in a square metre"

;)

Ooops :-(

You probably meant cubic metre?

Ouch, yes I did

We study it in high school.

It's common knowledge here; in the UK I was taught it in two classes at school: Science and Cooking.

We are taught to use the scales for measuring ingredients - and thanks to this trick you can weigh water (and milk) and vegetable oil (using 5-10% less) if you don't have a measuring jug.

> I suspect that only a minority of people in metric-using countries -- those with basic chemistry knowledge fresh in their mind -- know that "one milliliter of water occupies one cubic centimeter, weighs one gram, and requires one calorie of energy to heat up by one degree centigrade".

They taught us that in 4th grade in cooking classes. Then they made us remember that in physics and chemistry classes 2 years later.

There are plenty of things that everyone learns in 4th grade that not everyone remembers.

The point is that this particular concept of metric units is taught really well (repeatedly on many practical examples and then evwn theoretical ones) and so virtually everyone knows and uses it. It's deeply ingrained in cooking books, recipes, etc.

Of course I don't remember a lot of things from the 4th grade. This one stands out.

And least I forget, because nobody mentioned it, yet, what about the beauty of the DIN A papersize? It has been adopted as an ISO, even! Where everything is simply a half of the previous size.

You know what is worse than either metric or imperial?

Having both in use simultaneously like we have in Canada, where we work with lots of things manufactured in the US or in Canada for export to the US.

So any technician will have to have both metric and imperial tools, occasionally things of very similar size will get interchanged accidentally - using a 3/4" socket on a 19mm bolt for instance, which will work for a while but eventually round off the head because 3/4" is slightly more than 19mm.

I think we can all agree that mixing systems of measurements is the worst possible thing you can do with measurements. Just ask NASA...

(Look up what happened to the Mars climate orbiter)

F is not superior to C, your argument for it makes very little sense, even from a plain human "everyday" (non-scientific) point of view. Can anyone sense when the temperature changes by a single degree in F? I doubt it. With C you have a chance. With C when it's below zero you know there could be snow and ice.

Each set of 10 degrees in C is a pretty clear temperature range. 30-40 scorching. 20-30 hot. 10-20 warm. 0-10 cool. -10 to 0: cold

For me. 26+ scorching. 25 perfect. 24- freezing. Haha.

I feel almost the same lol. Without looking at my "smart" thermometer (is set at 24), I know what temperature is in the house. If it's 23,9 i'm already cold and I have to put something on. But if it's 24,1 I can stay with my shirt on.

You're just familiar with it - as somebody who has grown up with the metric system, I feel exactly the same affection about it, and to me imperial units feel stupid, unworkable and old fashioned.

I think this is the biggest problem with metric/imperial arguments - most of it is actually based on emotional attachment deep down.

> I also think that F is seriously superior to C.

Yeah, no. You're just suffering from Stockholm Syndrome or being thinly ironic.

People have absolutely no problem associating numbers to temperature sensations in C. And actually people can objectively feel temperature differences from around 2C/5F so in that way C is superior to F, 1F difference is meaningless.

> I also think that F is seriously superior to C.

Both are not metric though. Metric unit for temperature is kelvin.

True although C is just an offset from K, i.e. only absolute values change, temperature deltas are the same in C and K.

Just as a side note, the US system gets worse and worse when you look beyond the everyday units of measure.

Sure, inches are great, but below 1/4", screws are in a numbered system (higher number is larger) while the corresponding drill bits are in a different numbered system (higher number is smaller) or lettered (A to Z). Wire and sheet metal gage numbers are still different.

An #8-32 thread takes a #29 tap drill...

https://www.lincolnmachine.com/tap_drill_chart.html

0 C = frozen, be careful

10 C = you need a jacket

15-25 C = great outdoors temperatures

20 C = good house temperature in the winter

25 C = good house temperature in the summer

30 C = too hot to go out doing physical activity, good for a picnic or a day at the beach

35 C = too hot to go out, period

40 C = hot bath

100 C = boiling water

I'm glad you made this point, because I am the one that usually does and gets hammered for daring to even hint that imperial might not be totally insane! The temperature one I've always found compelling. Most humans only rarely experience temperatures outside of 0-100F. That makes sense to me. Celsius makes little sense, except for 0 being when water freezes. It compacts the scale too much for everyday use.

However, beyond basic human usage, I quickly switch to metric for anything involving actual math: simulation, science, finance, etc.

A "cup" is about what a normal drink is. A liter is an insane amount of liquid for everyday use. I don't sit down and drink a liter of wine, I have a cup of wine.

A popular unit for a large beer is the "40" which is what a 40 ounce bottle of beer is called. About 1.2 liters, but not a size found in "respectable" households.

The last couple of years we have had between -36 F to 97 F. Or -38 to +36 C. I like to be able to tell when the roads might get slippery (below +3 C or so), when the car will get problems starting if you forgot to plug in the heater (about -25 C), When it's time for the shorts (+18 C?).

Also handy to know that I need 3-6-3 ammounts to make pancakes. 3 eggs, 6 litres of milk and 3 dl flour (that will be meassured with grams because easier, can just pour everything into the bucket and press "tara"). Flour weighs 60 g per dl. Put bowl on scale, start it. Pour flour in the bowl until it reads 180 g. Reset and pour in milk until it says 300 g. Mix until perfect. Add eggs. Reset scale and pour another 300 g and mix again. Start frying!

10 can easily be divided by into fifths.

Thank you.

I'm glad I'm not the only person who thinks this way.

The strength of the metric system shows when you need several different scales. nano- micro- milli- kilo- mega- giga-

The number of inches in a mile is harder to get than the number of millimeters in a kilometer or grams in a ton.

Celsius and Fahrenheit may be use for some thing, but I think kelvin is a good system, even if others are use for other purposes sometimes (such as Fahrenheit for oven temperatures).

You should be careful about the term "imperial". US customary units do not always match the old British "imperial" units. A US fluid pint is significantly smaller than an Imperial pint, for example.

It's stunning to see people debating "ease-of-understanding" of the base 12 imperial system while at the same time happily using a decimal based currency (nearly?) all over the world.

It's easy to understand construction and cooking concepts in imperial? But you just used a decimal based currency to buy the materials for the said uses, and could easily add up the costs of those materials in your head instead of staring blankly at the cashier who was trying to add 77 shillings and 23 half-crowns.

No, it were actually pirates at fault of America not adopting metric: https://www.npr.org/sections/thetwo-way/2017/12/28/574044232...

Where I'm from, it's a hybrid system. kg, celcius, litres and inches

The actual text of the resolution, for those with low tolerance for dumbed-down PR releases:

https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN...

I have low tolerance for long ass papers ;)

But it's only three pages long :(

In a large font, and with enormous margins, no less.

Sorry man, I thought it would be like GDPR lol

Isn't that just toilet paper? (long ass-papers)

One of the OG xkcd's: https://www.xkcd.com/37/

How would you use the new definition to calibrate instruments? My current understanding is that there is a lineage of artifacts calibrated against another artifact until one of those was calibrated against the one true artifact. So how would NIST or another certifying source say that my 1kg standard is 1kg +/- tolerance?

Is it anyone with a kibble balance can now certify calibrations? How do you know your kibble balance is as accurate as the next guy's kibble balance?

https://www.nist.gov/si-redefinition/kilogram-kibble-balance

Edit: Found some information explaining this from NIST: https://www.nist.gov/si-redefinition/kilogram-disseminating-...

Don't miss the video for the DIY Lego watt balance.

https://www.nist.gov/si-redefinition/nist-do-it-yourself-kib...

Essentially this brings it one more step away from using another artifact for calibrating things. Instead this lets us define the kilogram against what we believe are universal constants, in this case properties about the electromagnetic force.

It's much simpler to understand looking at it with a watt balance, even though it's not going to be as precise or accurate as a kibble balance [1]. Basically now anyone with access to a kibble balance and the right set of numbers/information can make an exact 1kg object.

[1] https://www.youtube.com/watch?v=ewQkE8t0xgQ

I'm pretty sure a watt balance and a Kibble balance are the same thing. Regardless, that YouTube video is so good! I was just about to post the same link.

Or potentially more usefully, ascertain an accurate measurement of how closely a given measuring device is to the target to calibrate it's use in actual measurements (outside of the expensive validation mechanisms).

It will still mostly work the same way, except that instead of someone having the "one true artifact", anyone with enough equipment can measure their kilogram against natural constants and know it's correct.

It means the right answer is freely available to anyone (with a bunch of scientific equipment).

The pictures in that article about NIST reminds me of the adage, "The smaller the measurement, the bigger the lab."

I like to use metrology labs as an example of something people often take for granted (measuring things) and showing how deep that invisible rabbit hole goes.

To abbreviate - these definitions change the means by which those calibration artifacts ("transfer standards") are created.

The NIST explanation of Kibble balance calibration includes this:

> Everything on the right side of that equation can be determined to extraordinary precision: The current and voltage by using quantum-electrical effects that are measurable on laboratory instruments; the local gravitational field by using an ultra-sensitive, on-site device called an absolute gravimeter; and the velocity by tracking the coil's motion with laser interferometry, which operates at the scale of the wavelength of the laser light.

Current is measured in amperes, derived from the charge (in coulombs, defined from the charge of a proton) and time (in seconds, defined from the vibration of a Cs atom). Gravitational acceleration is measured in ms^-2, derived from length (in metres, defined from the distance travelled by light in a vacuum in a second) and time. Velocity is also derived from length and time.

With these new defined constants (including the Planck constant), all of the instruments could now be calibrated by observing natural phenomena and a whole lot of counting.

This is probably the dumbest thing I'll type on HN.

In university I just gave up trying to understand why we even needed the Avogadro constant / mole as a fundamental constant. It still confuses me. Why have a difference between molar mass and mass? Why couldn't it just be "1" and everything else change around it?

For the same reason count is not a mass. Avogadro constant is a count relating number of specified atoms to mass.

Isn't this something essentially tautological though?

When we discuss the mass of a neutron and we say "one neutron weighs one u" then we discuss the mass of an electron and we say "one electron is 5.4858×10−4 u" and "one proton is 1.0072764 u" then we add them up and say "one hydrogen atom is 1.00794 u while one helium atom is 4.002602" (forgetting some complications for a moment) are we not just summing likes?

Or is it just that since mass is defined in Planck and time / distance terms that we need to relate it to counts of things? Theres a gap there I don't understand. Can we not just say "we measured a proton's mass and it is u"? Am I making a jump there?

In my opinion it is because a mole is a numerical amount of atoms vs the mass of the substance, so it makes reactions, formulas, and measurements easier to determine. Avogadro's number is useful just as a baseline to use (number of carbon-12 atoms in 12 grams of carbon-12), like there are 12 inches in a foot or 100 centimeters in a meter...

... except if you take 6 two-inches you'll see something different than 12 one-inches. Our universe is weird. Defect of mass and stuff

In a meta-sense, I don't think your question is dumb at all.

There's a complicated technical topic which you're still not understanding. There's no indication it's a question you could easily answer yourself, and you're posting it in a forum of people likely to find the topic interesting, some of whom might give an answer that clicks for you.

Well done, IMHO.

It's not a fundamental constant.

> the Avogadro number was initially defined by Jean Baptiste Perrin as the number of atoms in one gram-molecule of atomic hydrogen, meaning one gram of hydrogen. (from Wikipedia)

(It's since been refined to be 12 grams of carbon-12.)

So a mole is defined to be approximately one gram worth of protons and neutrons. We use it because grams are a significantly easier unit of mass for humans to work with, than like individual particles.

Read the OP. It is now a fundamental constant. (But you’re right if you’re referring to the status quo before).

No, it's not. Avogadro's number is a constant, but it's not fundamental - the only difference is that it's defined in terms of fundamental constants (namely, the Planck constant) now. It's still an arbitrary number defined in terms of the mass of a gram.

Nope, it is fixed to be N_A = 602,214,076,000,000,000,000,000 exactly (6.02214076x10^23 to units precision).

It used to be the case that the mole was an experimental value equal to the number of atoms in a certain mass of a certain something. That is no longer the case with this revision. It is a fixed, never changing integer constant.

This does mean that 1 mole of carbon-12 is no longer exactly 12 grams. But it is approximately 12.0000000 grams, which is within the best we can experimentally measure today, so nothing changes in practice as a result of this update except first chapter of an introductory chemistry textbook (good excuse to push out a 9th edition for $250!).

Therefore it is accurate to say now that whereas before the Avogadro's number was experimentally determined based the exact expressed mass of a carbon-12 atom relative to a platinum-iridium cylinder in Paris (the old kg), it is now the case that the expressed mass of the carbon-12 atom must be measured relative to the a kg definition based on Planck's constant.

(I say "expressed mass" because this situation is a little confusing... I'm talking about the numbers we write down expressing the mass as a multiple of some standard kilogram. That reference mass changed, not the actual inertial mass.)

EDIT: Or you can just read the draft of the agreement that was voted on. The definitions are on the first page:

https://www.bipm.org/utils/en/pdf/CGPM/Draft-Resolution-A-EN...

No, that's not the part we disagree about. Yes, I know, Avogadro's number is a fixed constant now. It's not a _fundamental constant_:

https://en.wikipedia.org/wiki/Fundamental_constant

A fundamental constant isn't just any fixed constant. It's specifically a constant that describes a fundamental property of the universe.

For instance, c describes the speed of light in a vacuum, and is a fundamental physical property of the universe.

Avogadro's constant isn't the same thing. It's just a number that humans decided would be useful. We could have fixed it to any other number; there's nothing fundamental about the number ~6.022e23.

Fair enough. I was using a different definition, but arguing over definitions isn't a good use of time :)

I thought it was just a ratio. Mass per mole. I admit I have never used this in my day to day life and college was 20 years ago. So maybe I am clueless.

Nah, I think that's just it. It's easier to write down certain calculations in mole in a chemical context, because you're concerned with atoms reacting with each other. You don't have 12 grams of carbon and 4 grams of hydrogen, but 1 mole of carbon and 4 mole of hydrogen.

If it makes you feel any better, I've asked the same thing before.

My understanding is that the cause is error propagation. We can measure certain kind of masses really accurately in unified atomic mass unit. With better relative precision than the Avogadro constant. But if we used kilograms to write down these quantities then they would carry the error of the Avogadro constant needlessly.

Edit: I think your question boils down to "Why do we have two separate units for mass, u and kg, connected by the Avogadro constant?" Most answers dismiss your original question as Avogadro constant is not a unit. But u is a unit and it's the point why we have this constant.

Edit2: To further emphasize my point look at the mass of neutron[1]. It's listed both in kg and u. Note the number of decimal places.

[1] https://en.wikipedia.org/wiki/Neutron

Right, I get that, and if anything I feel less dumb now that I've asked it publicly and people seem to think that it's a non-dumb question, but when talking about fundamental constants I understand there is a practical nature to it all, but just as we have a nano-meter and a light-year I figured we'd have the same for mass.

Why do I need both kg and u as fundamental constants?

I believe the comments here have answered it. It isn't something weird, like quantum gravity or some such. If I understand everyone correctly it's just a practical decision we made at some point because we didn't want mass to be in u and that's that.

I feel better about it now.

They aren't fundamental constants, they are fundamental units. The system is ultimately about allowing people to compare measurements (not describing the universe in abstract), and is only tied to fundamental physical constants where it makes that more reliable.

That's not a whole answer, but it may be helpful for your thinking.

As others have noted, knowing the count of entities (note: not atoms, entities - i.e. it can also be molecules) in relation to actual mass is very useful for the physical sciences - at a molecular level the quantities of molecules and atoms interacting matter, not their masses - but mass is the unit I do experiments with.

EDIT: A simple example would be if you were trying to make water - H2O, from hydrogen (H2) and oxygen (O2). The molar ratio is 2:1 - but in doing a practical synthesis, that doesn't tell me how much mass/volume of gases to actually mix up. Avogadro's number and molar mass is what I need to turn those into practical units to work with.

I think what the commenter is referring to is why use Avogadro's number instead of say, just Sextillions or Septillions.

I mean that really comes back to the "practical units" thing (and that chemists were the ones doing the work) - a kilogram of anything in chemistry is a huge amount, whereas a gram is about right to make "a lot" of something (in synthesis research people get excited about gram-scale synthetic yields).

So it's pretty much chosen to get integer-ish units with common things you work with like carbon - i.e. 1 mole of carbon of is ~12 grams.

Yeah, that makes sense (:

Simplistically: two moles of protons+two moles of neutrons do not weight the same as a mole of nuclei of He-4, as far as I know.

No I agree, it seems stupid. What we did is take a block of metal and call it a kilogram, figure out how many atoms are in 1/1000 of it (a gram) and call that a mole. What we should do is redefine the gram to be whatever 1e10 atoms of Hydrogen weighs, or something similar. When I read the headline I thought thats what they did, and I admit first reaction was "oh god I'm going to be dealing with conversions and associated errors for the rest of my life".

Disclaimer: I took high school chem, that's it.

1E10 atoms of hydrogen isn't a fixed mass.

Cf binding energy, electron excitation, E=mc^2 (the m there is m0, the rest mass; the full equation includes the momentum and "relativistic mass").

The situation is actually worse for hydrogen (cf hydrogen bonding).

http://math.ucr.edu/home/baez/physics/Relativity/SR/mass.htm... is a pretty coherent and readable approach to the subject.

> What we should do is redefine the gram to be whatever 1e10 atoms of Hydrogen weighs, or something similar.

That was actually an alternative proposal for redefining the kg. The kg would have been 1000/28 the weight of a mole of silicon-28; you could build a sample by counting 6.023x10^26/28 atoms of silicon-28, and making a sphere out of them.

Initially the watt balance seemed to be less precise than atom counting, but then it was improved to a point where defining the kg on top of the mole became less convenient than the definition they are adopting now.

leni536’s answer is the real answer but I’ll give you another more meta one:

Because the SI system is redundant anyway one constant more or less doesn’t matter much.

If you want a truly minimalist system you can use CGM or MKS.

In chemistry, the molar “mass” plays a more important role than the mass proper. Why has its unit not been chosen to be equal to 1? For the same reason as why the gram is not defined to be the mass of, say, proton. (Chemistry doesn’t normally deal with single molecules.)

For the same reason that we use both temperature and energy and find them both useful. We can talk of the energy of an electron. On the other hand, temperature, is an statistical property defined for many particles.

Using mole (based on Avogadro constant) makes it easier to do statistical mechanics, but it's not a microscopic property like mass.

Understanding mass in molar terms is necessary to do a lot of chemistry correctly. The mole is effectively a count of the number of molecules kicking about, although the count is large enough that terms like "quadrillion" don't cut it. (One mole is about 600 sextillion molecules). Knowing how many molecules are around lets you actually compute how much stuff can react in a given chemical environment, and other aspects of chemistry end up being pretty related to molecule counts. Vanilla mass doesn't cut it since an atom of iodine weighs about 6.6 times that of fluorine but can still only react with one other molecule.

The flip side is that the molecular count is less useful to us in the everyday world. We can gauge the weight of a kilogram much more than we can gauge a septillion molecules. And if we're trying to figure out how much stuff a shelf can hold before it collapses, it's the weight that matters, not the actual molecular count. (Note for pedants: in the familiar environment of Earth's surface, mass and weight can be treated as the same quantity in most cases.)

So mass and molecular count are both very important quantities that have importance in different fields of science, and they don't have a trivial relationship to each other. Avogadro's constant and molar mass is a way to express their relationship.

trying to use kg instead of moles when calculating a chemical reaction would be like trying to set up a speed dating event by taking the weights of all the men and women instead of matching them up pairwise. Sometimes it is much easier to calculate based on scalar quantity than it is to calculate based on mass.

The argument there is that avogadro's constant is just an arbitrary number and mol is not an unit, but weird case of SI prefix.

On the other hand it is fundamental-ish constant, because it is defined as arbitrarily scaled result of inherently uncertain measurement. And the new definition of kilogram had significantly increased the attainable certainity of such measurement (to the extent that it is uncertain due to practical issues, not by definition). The other proposed replicable definition of kilogram (ie. mass of Si monocrystal wih particular geometry) would fix the definition of mole as some known and defined number, but would be significantly harder to replicate (because it would define how to produce an artifact in contrast to how to directly measure the mass as the ratified definition does)

I think the GP is making the claim that Avogadro's constant should be 1 (effectively eliminating it), not that there's no need to count molecules.

Yeah, I think that's his idea. So, instead of tables of molar mass in g/mol, you would have tables in terms of "amount of substance"/g. E.g. number of atoms or number of molecules.

An Avogadro's constant number of molecules is one mole. One mole of hydrogen has much less mass than one mole of iron. You have to choose an arbitrary mass of a single element as the base quantity. Hydrogen might be the best theoretically, it's just a proton and an electron, but it is tricky to work with because it's a gas at room temperature. So instead the mole has been defined as the number of molecules in a specific mass of carbon-12.

Carbon 12 is being used because that accounts for the nuclear forces which are absent for H-1.

I think this is exactly the rationale. But, from a more practical perspective...

If instead of g/mol, we referred to molecules/g -- we would end up populating tables and charts with really big numbers. This would make lookup tables hard to read, difficult to publish, and hard to work with. Imagine if you had to do math with a bunch of 10^23 exponents all of the time.

Instead, it was agreed to effectively pull out a constant value from each of those to make the math significantly easier. Now, instead of dealing with a lot of big numbers, all of the lookup tables could now list smaller g/mol values. And we would be left with just the one single large (Avogadro's) number in the equations.

Honestly, we don't need a set mole constant, but it makes chemistry significantly easier to do so. Unlike the other constants mentioned in the OP, Avogadro's number is completely arbitrary. It could be '1' as the parent suggested, except then it makes the rest of the math more difficult.

Even for this SI overhaul, we didn't really even need to redefine the mole, except for the fact that it was previously defined in terms of the old kg. This was just "fixing a glitch".

> Imagine if you had to do math with a bunch of 10^23 exponents all of the time.

What if it was just set to 10^24 then? Much easier to remember and serves the same purpose.

If it was 1 it would work too, since the SI system already has a way to deal with large numbers: prefixes. So we might wrote Ymol for yotta mole = 10^24 mol.

Then 1 mol of carbon-12 would weigh 1300 g rather than 12 g and the conversions would be a pain.

> Even for this SI overhaul, we didn't really even need to redefine the mole, except for the fact that it was previously defined in terms of the old kg. This was just "fixing a glitch".

I came to complain about the article calling the mole a "base unit of the SI", and this seems like an appropriate thread.

Why is the mole a defined unit at all? As far as I understand things, "one mole" is the same thing as Avogadro's number -- neither can be a unit, because they're both dimensionless constants (well, they're both one and the same dimensionless constant). Applying actual units, "one mole of water molecules" is the same thing as "Avogadro's number of water molecules". Avogadro's number, and therefore the mole, is the conversion factor between atomic mass units and grams. Similarly, 3 is the conversion factor between feet and yards, but nobody thinks 3 is a fundamental base unit of the imperial system. The foot is a base unit of the imperial system, measuring length, the yard is a non-base unit also measuring length, and 3 is a number with no special relationship to the system at all. It would be total nonsense to say that yards are defined by reference to 3. How is Avogadro's number different?

Wouldn't "fixing the glitch" be abandoning the idea of calling the mole a unit in the first place?

The new definition of mole is exactly that - it's just 6.02214076×10^23 items of whatever, and no longer depends on kilogram.

That's not a base unit, or a unit of any kind. What's it doing in a list of SI base units?

It is a base unit, a unit for lots of stuff, and it is not dimensionless it is 6*10^23/mol

I'm pretty sure the mole is not defined as 6 * 10^23 mol^{-1}.

There is a concept of "the Avogadro constant", which is defined to have units of mol^{-1} (at least, according to a cited statement on wikipedia), but that is not a coherent concept -- since mol is dimensionless, mol^{-1} is also dimensionless.

Just look at https://en.wikipedia.org/wiki/Mole_(unit)#Criticism :

> Since its adoption into the International System of Units in 1971, numerous criticisms of the concept of the mole as a unit like the metre or the second have arisen:

> the number of molecules, etc. in a given amount of material is a fixed dimensionless quantity

> the mole is not a true metric (i.e. measuring) unit

Or look at https://en.wikipedia.org/wiki/Atomic_mass_unit :

> One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is numerically equivalent to 1 g/mol.

amu and g are both units of mass, so 1 amu = 1 g/mol is an explicit statement that mol is dimensionless.

Calling mol a unit won't accomplish anything except corrupting your dimensional analysis. mol is not analogous to the SI units meter, second, ampere, gram, kelvin, etc. -- it is analogous to the SI prefixes kilo-, mega-, milli-, micro-, nano-, etc.

Or you can say it is the conversion between a gram and a dalton, which is the same but more complex as it is now intertwined with the gram

I already said exactly that:

>>> Avogadro's number, and therefore the mole, is the conversion factor between atomic mass units and grams.

But that doesn't intertwine anything with grams. I went on to say

>>> Similarly, 3 is the conversion factor between feet and yards, but nobody thinks 3 is a fundamental base unit of the imperial system.

>>> It would be total nonsense to say that yards are defined by reference to 3.

Why does it need to be based on the mass of an arbitrary molecule? Can't it just be 10^23 or 10^24? Most of the time, you're going to have to look up constants to convert moles to mass anyways.

Avogadro's constant is not itself a heavily-used value in chemistry. Its derivation is obvious if you think in a different way:

You need to convert from mass to numbers of molecules, which means you need to divide it by the mass of a molecule. The mass of a molecule is determined by the sum of the weights of each of the atoms, themselves the weights of their constituent nucleons [1]. If you fix the weight of a nucleon to be 1 (that is, we measure in daltons), then computing the weight of a molecule such as glucose (aka C₆H₁₂O₆) in daltons is a trivial formula. All you need is a periodic table that lists atomic weights, which is every copy you find a chemist using. It's worth noting that the resulting molecular weights are going to be independent of whatever measuring system you want to use [2], whether it be grams, ounces, alien flits, what have you.

Now you need to convert the mass of your substance into a count of "stuff-loads" of molecules. The simplest and most idiotic thing to do is to define a "stuff-load" to be the amount of molecules in a unit mass if it weighs 1 dalton--in other words, you make this formula be exactly one. In SI, the unit mass for this equation is grams and the "stuff-load" is the mole. If we were using US ounces as the unit mass, we'd define an ounce-mole and use that instead of SI moles.

Put another way: we define a mole such that the constant in the computation of moles from molecular weight and mass is exactly 1. Avogrado's constant itself is merely the inverse of the mass of a nucleon when expressed in grams.

[1] Okay, there's a lot more that goes on into the computation of mass. In terms of the mathematical error, though, other sources of error (e.g., wrong isotopic ratio) are going to matter before these come up.

[2] Up to the slight adjustment (about ±1%) of what you consider the weight of a nucleon to actually be.

The one that made it click for me as incredibly useful was Avogrado's Law (now part of the Ideal Gas Law):

> Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules.

This law, for example, explains why hot air rises. Take two equal quanties of the same gas at the same pressure. They will have the same volume. Now, heat one quantity of gas. By this law, that gas will have a larger volume at the same pressure. Because it has the same amount of mass distributed over a larger volume, it must be less dense. Therefore, it rises.

> By this law, that gas will have a larger volume

The law as quoted doesn't say what happens when the temperature change. Maybe it gets more dense? Be more specific.

> By this law, that gas will have a larger volume at the same pressure.

It will have larger volume, but that is not implied by Avogadro's law. That law is about the surprising property of all gases: no matter the chemical nature of the gases, if they all have same T and P, they all will have same number of molecules per unit volume.

Stoichiometry.

We need a means of converting mass to number of atoms so that we can predict how much mass of a specific product will be formed, what the limiting reägent will be, &c.

It also helps to define concentrations based on number of moles in a L of solvent (Molarity vs g/L) for the same reason.

The candela is a real abomination of a unit.

Absolutely, it's candelous that it's part of the standard.

Historically, the mole predates the acceptance of atomic theory. Stoichiometry of various reactions let you work out that there was some mass of oxygen that would entirely react with some mass of carbon to form carbon monoxide. They didn't have the same masses, but the relative amounts for each element were constant (or small integer multiples, such as twice as much oxygen to carbon for CO_2).

So Dalton took the lightest one, hydrogen, and defined a mole as the stoichiometric amount equivalent to that in 1g of hydrogen. Looked at that way, it's a pretty solid choice.

Well, now you could do that. At least you could next March when these rules take affect. But before you could not because the conversion between atomic mass and SI/kg mass depended on that experimental constant. Two mass systems were required because we couldn’t conver between them with atomic accuracy.

I don't believe the Avogadro constant needs to be an SI unit. It's like having 12 as an SI unit, or a million, or 1. Sure, it's a useful constant scaling factor, but it doesn't need to be canonized at the heart of the SI system. It doesn't actually express anything fundamental about how we measure our universe.

And if nothing else, it can be derived: a mole is the number of atoms in a kilogram of carbon-12. Done.

> And if nothing else, it can be derived: a mole is the number of atoms in a kilogram of carbon-12. Done.

No longer is. Not quite.

> why we even needed the Avogadro constant / mole as a fundamental constant(...?)

It serves as a link between human-scale and atomic-scale observations, classically needed for chemistry performed on Earth by humans. This link must exist, as others mentioned, for stoichiometric calculations (e.g. air/gas mixture in a internal combustion engine). For much of modern scientific history, it was deemed useful to scale into an easily eye-visible human scale (the gram). [0]

[0] https://en.wikipedia.org/wiki/Avogadro_constant#General_role...

The number of things in a mole is arbitrary. It's a dimensionless unit. However, since many things are already measured in moles in chemistry, there's no real reason to remove it. Dealing with numbers on a more practical macroscopic scale is probably more convenient than dealing with large powers of 10.

https://en.wikipedia.org/wiki/Mole_(unit)#Criticism

I get that this is a significant milestone but this seems extremely overstated:

"the new changes will have wide-reaching impact in science, technology, trade, health and the environment, among many other sectors."

Am I missing something?

I don't know about trade, but kilo standards were deviating by tens of micrograms from eachother, some things are sold at prices which warrant accounting for those micrograms, so a completely stable international definition seems helpful.

Certain types of scientific instrument will need to be recalibrated to meet the new definitions.

Is there any scale in the world that can measure a kilogram to within the accuracy of a microgram?

And if you buy a kilogram of something and they accidentally short you by a few micrograms, haven't you only overpaid by a few parts per billion? Even on a billion dollar order you've only overpaid by a few dollars...

For your first question some Kibble balances have accuracy parts per billion in measurement of the kilogram.

For your second question, agreed - no trade deals care about the accuracy of the new kilogram vs old.

I agree that nobody cares for this level of precision in comercial trade, but as a thought experiment ...

According to the first result in Google https://brightside.me/wonder-curiosities/the-16-most-expensi...

> 1. Antimatter — $62.5 trillion per gram

> 2. Californium — $25-27 million per gram

So the difference is a few dollars per milligram of antimatter, and less than a cent per kilogram of Californium.

From https://en.wikipedia.org/wiki/United_States_Bullion_Deposito...

> As of November 2017, Fort Knox holdings are 4,582 metric tons (147.3 million oz. troy), with a market value of over $100 billion.

So the difference is a few hundred dollars.

Your math is off..... 62T / 1g = $62B /mg = $62M/ug.

$100 million dollar rounding error.....

If you're buying 1 milligram of a substance, how much are you affected by an one microgram error in the definition of a kilogram?

Hint: not by one microgram.

Mostly yes, it does seem over-stated. I guess if you squint "wide-reaching" does not necessarily mean "important" just, you know, "wide-reaching". Like the "wide-reaching" effect of dropping a pebble into an otherwise undisturbed swimming pool maybe? The ripples go pretty far, they don't really matter, but they do go far.

With the old definitions, the values of the known constants were just approximations, but now that the unit is defined based on the constants, we can consider the constant as being the exact value, no matter how imprecise it was when it was measured using old definitions of the units.

So it's the equivalent of removing a magic number from your code and putting it into a const variable.

I read the uk address and was afraid they had voted to leave the metric system, as some sort of Brexit associated madness.

Veritasium did a great video [0] on this leading up to the vote.

[0] https://youtu.be/c_e1wITe_ig

I wish he would spend a bit more time exsplining were some of the constants come from, although that would probably make the video a bit weaker overall. Wasting time on such information.

He's probably done videos on many of them already.

Recently I have been thinking about if any of our units makes sense in cosmic perspective. Let's take speed of light for example. It's approximately 300000 km/s. But then what is a second? It's 1/60 of a minute which is 1/60 of an hour which is 1/24 of a day(and so it goes) and all those numbers are arbitrary. A day doesn't make any sense outside our planet anyway, I doubt that there is another celestial body in the universe that takes the same time to complete a rotation. Period of some natural phenomena (like atomic electron transition) sounds better as a unit but it's a really tiny period of time so we have to scale it to make it practical for us. We will use decimal numeral system to do that, another arbitrary choice. What if we had 12 fingers or 8? This can be extended to all kinds of measurements so I wonder if any of this would make sense to another civilization. What would a cosmic system of units would like? Any reading about this would be greatly appreciated.

The definition of a second isn't based on the Earth's motion, but some natural phenomena like you recommended. "The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom." [1]

[1] https://www.scientificamerican.com/article/how-does-one-arri...

Of course, that definition was made to make our current definition of the second continue to work.

"The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom."

Yes I think you're mostly correct, it's all pretty arbitrary. An alien civilisation is going to need units of length, time, speed, mass, energy etc..

Speed has an obvious unit which is the speed of light (in a vacuum), which seems to be the same everywhere.

All the others are a bit more arbitrary I guess.

Sounds like you're looking for Planck units. https://en.wikipedia.org/wiki/Planck_units

I would suggest that Planck units scaled by powers of 2 is the closest we can get to a cosmic system of units. The choice of binary is non-arbitrary as it's the smallest base that can be chosen and still provide scaling.

You might be thinking along the lines of natural units [1] or even Planck units [2], where you set some fundamental constants to 1 and take it from there.

[1]: https://en.wikipedia.org/wiki/Natural_units [2]: https://en.wikipedia.org/wiki/Planck_units

The Wikipedia entry is pretty informative https://en.wikipedia.org/wiki/Proposed_redefinition_of_SI_ba...

Very cool explanation of the math as well as the concept behind the standard:

https://www.youtube.com/watch?v=Oo0jm1PPRuo

Has a "metric" version of time ever been proposed? Seems odd to me that we're "ok" with divisions of 12 for time but not length.

I guess for science seconds are basically the only measure of time that usually matters?

Metric had time from the start. However it was work 4 days, 1 day weekend. However the loss of personal time was very unpopular so it never caught on.

I'm not sure why a metric hour didn't catch on.

I think I'm missing the joke. Mind explaining it?

No joke, except I was referring to decmial time not metric time. https://en.wikipedia.org/wiki/Metric_time https://en.wikipedia.org/wiki/Decimal_time

a 7 day week gives two days weekends every 5 days, so you quickly lose personal time on the 4 day week.

Seconds are the metric unit of time if I understand it correctly. It doesn’t make any sense to say “kiloseconds” or something like that because days are the time that the sun is up (ish), months are roughly based on moon cycles, and years are approximately the time it takes us to go around the sun.

It’s also historical and pretty hard to change the basic units of time.

FWIW, while scientists don't usually use kiloseconds, it's pretty common to see 1.437e4 seconds, rather than 3h 43min 20sec, used as units in time series etc. Similarly one uses milliseconds, femtoseconds, and soforth.

Years (or more specifically millions of years) gets used sometimes when talking about astrophysics, evolution or continental drift. (I am not a researcher and definitely not in any of those field though, so this may just be in material aimed at non-scientists). But I guess there's enough orders of magnitude of different that they rarely cross over so no one cares about the odd ratio, similar to J vs eV.

There has been a proposal during the French Revolution with 10 hours a day, 100 minutes an hour and 100 seconds a minute. But it has only been in use for a few years beginning in 1792: https://en.wikipedia.org/wiki/Decimal_time

(10/24)(100/60)(100/60)=1.1574

Our biggest revolution yet: extending the length of the day by 16%!

Presumably, the second was shorter, rather than the day was longer.

EDIT: More specifically, if you take an average rotation of the Earth as 86164.1 seconds, and divide by 10, then 100, then 100, you get 0.861641, which would be the conversion from our seconds to the metric second in that scenario. Likewise, the metric minute would be 86.1641 of our seconds or about 1.43607 of our minutes, the metric hour would be 8616.41 of our seconds or 143.607 of our minutes or 2.39345 of our hours. The day would be slightly shorter than our day, reducing the need for leap seconds to keep our time aligned with the sun.

You could just define the second to be a 1/100,000 of a day and go from there. Aside from screwing with literally everyones perception of time, it could work.

But which day? Such a second would probably work for everyday purposes (just like to most of us a second is 1/86400 of a day) but it would be woefully inadequate as a universal fundamental unit of time. And defining the second in terms of something like "the length of the solar day at Greenwich meridian on Jan 1 2020" prevents anyone from ever reproducing the exact value based on their own measurements, which is one of the big reasons for defining fundamental units in term of physical constants.

This is especially true when you have things like large earthquakes[0] changing the rotational speed of the earth slightly.

[0]: https://www.nasa.gov/topics/earth/features/japanquake/earth2...

Yep, things leap seconds have been used for. The moon also constantly robs Earth angular momentum via tidal interactions.

But an even bigger issue is that the sidereal day (one 360° rotation of Earth as measured against distant stars) is not 24 hours but roughly four minutes less. And the length of the solar day also varies over the year due to the slight eccentricity of Earth’s orbit—days near perihelion are slightly longer than near aphelion. And then there are the higher-order effects caused by gravitational interaction with other planets...

One can arbitrarily define a second as anything and then say that one UTC day usually has 100000 seconds and some are longer or shorter. It is just a matter of scaling few unit definition constants by 10000/86400.

Yeah, I don't think it's really an issue. Physicists only convert things to hours/days/years when disseminating results to a broader audience, when doing the actual physics everything is microseconds or megaseconds or whatever.

24 and 60 do make sense because they are highly composite numbers: https://en.wikipedia.org/wiki/Highly_composite_number

You could say the same thing about most Imperial units, but most people still prefer the metric system.

I would say most people prefer the one they learned first. For doing science metric is usually better. Easier unit conversions. I think inches/feet are better for construction as you have more options at what level of accuracy you want to work with and splitting things up unless you need to have a fifth of something.

And to think, we could unify Imperial and metric if we just shift the whole world to a duodecimal number system! :P

That's actually exactly why I like working in Imperial when woodworking. You're composing and dividing things by 2 all the time, so a base-2 fractional system is great.

12 and 60 are superior highly composite numbers¹ — as is 360, the number of degrees in a circle and the number of days in a year (with a little engineering work TBD).

Speaking of circles, SI hasn't fixed Hz vs rad, have they?

¹ https://en.wikipedia.org/wiki/Superior_highly_composite_numb...

> Speaking of circles, SI hasn't fixed Hz vs rad, have they?

I don't think so.

Anyone who hasn't heard of the Hz/radian issue should see the "Hz" definition in the units definition file shipped along with Frink - if you like finding interesting rants in unexpected places, it's delightful:

https://futureboy.us/frinkdata/units.txt

Appropriately, it now contains several outdated rants, showing vast impact these redefinition have: we'll all get an update to units.txt soon!

Heinlein's "Starship Troopers" has the space marines using "kiloseconds" and "megaseconds" conversationally, and it was always tricky for me to convert those to hours and minutes in my head accurately.

Odd choices... since 1000 seconds is ~17 minutes and 1M seconds is 4.6 hours.

> 1M seconds is 4.6 hours.

Really? :)

I think the parent meant 4+6i.

  $ units --verbose
  Currency exchange rates from FloatRates (USD base) on 2018-10-25 
  3070 units, 109 prefixes, 109 nonlinear units

  You have: 1 megasecond
  You want: 1 day
          1 megasecond = 11.574074 * 1 day
          1 megasecond = (1 / 0.0864) * 1 day

Gee, I never knew about units, thank you. Very cool. It can convert meters/s to furlongs/fortnight, cm^3 to gallons.. Write fractions like '1|2'. And you can add your own units to the units file.

Also in the book "A Deepness in the Sky" by Vernor Vinge. In the beginning of the book there was a convenient chart for converting to our customary earthly time units.

And in Dukaj's "Perfect Imperfection" [1] occasionally multiples of Planck time are used (with metric prefixes), as the post-humans and "out-of-space computers" can operate on very small time scales.

[1] https://en.wikipedia.org/wiki/Perfect_Imperfection

I'm sure measuring "days" becomes silly when you're not spending a significant amount of time on a rotating spheroid orbiting a single star.

Rounding up to 4Ks is a reasonable substitute for an hour. Also gives you the convenient 15min ~ 1Ks or "a quarter of a metric hour."

In scientific literature we do typically use one particular preferred time unit (second being the SI units) and then exponentiating properly (eg optically driven metal to insulator transition in V2O3 occurs in 1.3 picoseconds (10^-12 s), desorption of atmospheric gasses from CoPc thin film in vacuum takes ~10^5 s (~1 day)).

Interestingly, a week can roughly be approximated as 10k minutes (with an error of less than 1%).

And a year is PI * 10^7 seconds (within 0.5%).

That's because the Earth's orbit is within 0.5% of a perfect circle.

(Just kidding.)

Yes, for science, seconds are sufficient (and metric). For everyone else, convenient computing of fractions is more important when dealing with time, so nobody seems to be interested in changing the time units: https://en.m.wikipedia.org/wiki/Sexagesimal https://en.m.wikipedia.org/wiki/Duodecimal

The French Revolution attempted a decimal calendar alongside their switch to metric. It's a fascinating artifact: https://en.wikipedia.org/wiki/French_Republican_calendar

Calendars are hard because you've got multiple inconveniently disparate sources of information you want to unite: universal constants on the one hand (such as the second being tied now to atomic vibration) and more "local" concerns such as the orbital position of the earth with reference to the sun, the moon, other neighboring objects in the solar system.

Vernor Vinge's novels, as one example, use metric prefixes and seconds exclusively (this is referred to as Metric time [1]), which is a fun thought experiment. The biggest complaints are that the units aren't necessarily great for human activities and definitely don't align well with minutes/hours/days/weeks/months.

Hectosecond is close to a minute, but slightly larger (1.666 minutes). Kilosecond is about 16.666 minutes long, which is the closest unit to an hour. It's almost a useful quarter-hour (but again it doesn't line up that well). But then you hit the order of magnitude wall and the next prefix up is Megasecond which is nearly, but not quite a fortnight (~11 days), and Gigasecond is just shy of 32 years. You long at that point for more prefixes between Kilo-, Mega-, and Giga- if you are using seconds as base unit at that point, especially living on Earth and trying to coordinate calendar weeks, months, years. (There are non-standard prefixes Myria- (10^5), also from the French revolution, and Hebdo- (10^7) which are almost useful enough here to beg them to be standardized.)

[1] https://en.wikipedia.org/wiki/Metric_time

Super interesting answer thanks!

Yep.

In Vernor Vinge's fiction, spacefaring humans even measure time in kiloseconds and megaseconds. 1 ks is slightly more than a quarter of an hour; 1 Ms is about eleven and a half days.

https://en.wikipedia.org/wiki/Swatch_Internet_Time

> Instead of hours and minutes, the mean solar day is divided into 1000 parts called ".beats". Each .beat is equal to one decimal minute in the French Revolutionary decimal time system and lasts 1 minute and 26.4 seconds (86.4 seconds) in standard time. Times are notated as a 3-digit number out of 1000 after midnight. So, @248 would indicate a time 248 .beats after midnight representing 248/1000 of a day, just over 5 hours and 57 minutes.

If we invent a system without timezones or daylight savings time I will adopt it in a heartbeat. I don't even care if it's not 10-based.

just set the timezone of your devices to UTC, and you're done! Actually getting other people to schedule meetings with you in UTC is going to be a bit trickier though.

It makes 'more sense' to change the metric system to be base 12, because base 12 is very nice.

And really, you can use kilo seconds or terra seconds just as easily as micro seconds. Its just harder to relate to as human time-scales.

>The definition of the kilogram for more than 130 years, the International Prototype of the Kilogram (IPK), a cylinder of a platinum alloy stored at the BIPM in France, will now be retired. It will be replaced by the Planck constant

Maybe I interpreted it wrong (non-native English speaker), but does it say that the Kilogram will be equal to the Planck constant? Shouldn't it be that the definition of the Kg will be based on the Planck constant?

>Although the size of these units will not change (a kilogram will still be a kilogram)

Are our current measurements of the IPK that exact so the old kg is exactly equal to the new Kg? How can they measeure it with 0 error?. It doesn't make any sense to me.

It's not just you, the wording is a bit weird. Yes, they are trying to say that the definition of the kg will be based on the Planck constant.

Further down, the article says: "The kilogram – will be defined by the Planck constant (h)."

> but does it say that the Kilogram will be equal to the Planck constant?

No, this statement means that Kilogram will give up its place as a fundamental unit to Planck constant. Earlier, Kilogram was used as a fundamental unit, defined by a physical object. Not anymore.

The kilogram will be defined by Planck constant. Namely, m = E/c^2 = hf/c^2.

> How can they measeure it with 0 error?

We can't, all measurements have errors. But we can measure things better than a physical object, which has changed with time. So we only have to measure Plank constant with precision higher than variation of physical object's mass for the purpose of replacing the definition of mass.

I guess it means that we are fixing the value of the Planck constant and deriving measure of kilogram from it. Given the measure of second and metre, a kilogram is the mass so that the value of plank constant is observed to be exactly 6.626x10^−34.

Finally there is order in units for science community. Hopefully such transformation will come to US one day.

The US units are defined in terms of SI since the Mendenhall Order[0], so they also benefit from this change.

[0]: https://en.wikipedia.org/wiki/Mendenhall_Order

It wasn't until 1959 that the yard was metricized. This still affects precision machinery manufactured before the changeover.

It was metricized with all the rest before that. What happened in 59 was harmonization with other countries including Canada, who had a different agreement on the metric yard. The older american definition was 1 yard = 3600/3937 meter. The international metric yard is exactly 0.9144m. (A difference of 0.002mm)

Never understood why the reference weight was one and not a maintained average over several or tens. This could have included aperiodic less used reference weights stored differently, different washing cycles &c.

I know several bipm participant nations had clones but they were always understood to be daughter weights.

Level surfaces (for instance) used to be made as triplets and never pairs: pairs can form lenses.

Not that a kibble balance definition isn't better: I just don't understand why the kg definition was a Singleton and not statistically satisfied.

Decay would be exponentially greater with more weights. Causing a larger decrease over time.

Except some kg reference weights gain weight. The washing regime ablates, but the metal matrix is porus at the atomic level (I am told) and so they accrete.

Therefore there would be gains and loses. Not just losses

So...How many Planck's is one Kilogram then?

>The mass of the international prototype of the kilogram m(K) is equal to 1 kg within a relative standard uncertainty equal to that of the recommended value of h at the time this Resolution was adopted, namely 1.0 × 10-8 and that in the future its value will be determined experimentally,

Is the Planck simply the most standard deviation the kilogram can stray from now?

This wikipedia section breaks down the new definition nicely https://en.wikipedia.org/wiki/Redefinition_of_SI_base_units#...

It is still not apparent to me. Is a kilogram of something now it's joules x seconds or something? Does the kilogram now vary depending on what the kilogram is of? Like, is a kilogram of Iron a different mass from a kilogram of Aluminum?

>The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10−34 when expressed in the unit J⋅s, which is equal to kg⋅m2⋅s−1, where the metre and the second are defined in terms of c and ΔνCs.

So mass is now some sort of length times a given elapsed time?

I believe it means something like:

Given the definition of metre and the definition of second, the kilogram is whatever value that makes the Planck constant h precisely 6.62607015×10−34 kg m^2 s^(-1).

But isn't that a bit of a recursive definition? What might one use as the value of kg in that example?

There is only one value a kg could be in that example, everything else is constant. The question I think you're trying to ask is "why 6.62607015×10−34 instead of some other simpler value" and the answer is a bit longer.

Original 1 kg was the mass of a cubic decimeter of water at 4 C at 1 ATM. Why a cubic decimeter at 4 C? Water is densest at 4 C and a cubic decimeter of it is a weight that people can work with on a day-to-day scale. Unfortunately this was a bit hard to measure so they made the IPK (international prototype kilogram) which was a lump of metal. Fast forward 100 years and the lump of metal proved to be too unreliable for modern standards as it kept losing very small amounts of mass, also it Earth's gravity isn't even so it requires you average it out and then calculate the local offset and a whole bunch of other weird things that can mean a microgram or two. This is inconvenient but we still needed a way to say "1 usefull measurement of mass" but unfortunately in the universe 1 Planck's constant is far too small to ever use daily. Thankfully it has become easier to accurately measure Planck's constant against the IPK so now we have solidified 1 kg to be exactly what we measured.

The nice thing is 1 kg will forever be the same thing now and is easy to measure to extraordinary accuracy. The downside I think you're asking about is 1 kg by itself isn't some significant relation of the physical world, it's just a useful-in-daily-life multiple of mass as defined by Planck's constant.

I can imagine that in 100-200 years we'll have to adjust some unit because our understanding of some constant was just slightly wrong.

According to the new definitions, some of the fundamental constants can no longer be wrong. We could even have defined them as 1 (which is what physicists have been doing for a long time already.)

If you do that, magnitudes of resulting units will either be huge or very tiny, depending on the composition of fundamental constants in said measure. The constants are very carefully chosen to match old units.

There are some theories of physics that imply that the value of "constants" like the speed of light actually vary slightly over long distances or times. This would be very inconvenient for the new system if it turned out to be true.

So there was a definition of a kilogram based on an actual physical thing with an arbitrary amount of mass.

Does this new definition essentially try to approximate that mass as close as possible? What is the margin of error there?

I would love to know this for a second as well, although I don't know what we used to measure a second before we locked it to the vibrations of a cesium atom.

The Earth?

Yes. In two ways.

First, the assumption was that the Earth's rotational period was 86400 seconds. Mechanical clocks had given us no reason to doubt this was so.

By the mid-20th century quartz timers were able to discern that the Earth has longer and shorter days, as numerous factors cause the spin to speed up or slow down. Instead of a single day the second was taken to be one 86400th part of an average day over the whole year.

A few decades later the availability of atomic clocks made this seem silly and we uncoupled the second from the variably spinning Earth. The completely arbitrary seeming atomic clock definition of a second was basically chosen to be indistinguishable from our last guess at the "averaged over a year" second.

Something I've considered recently is the case of estimating heighth (or any length) in customary vs. metric.

In the US, if I'm describing someone, perhaps to a police officer, I can fairly easily conceptualize the difference between 5ft, 5ft 6in, 6ft, or even smaller degrees of difference.

Though I'm certain this is likely just a result of me having grown up with the customary system, it seems like it would be more difficult (or at least more tedious) to estimate the heighth of a person using meters, given that most humans are in the 1.5-1.8m range (by my estimation). Especially when looking only at one gender, the range of possible heights is quite small in meters, requiring more precision to describe.

For example, I can reliably understand and visualize the difference between 5'0" and 5'4".

I'm curious for those in the rest of the world - can you meaningfully visualize the difference between 1.5m and 1.6m? Or perhaps 1.55m and 1.58m?

Well, sure we can. It is a matter of practice, like everything else

This is only due to you being used to certain units.

I was raised in EU using Celsius scale and can relate to full scale. In US I can relate only to 70-80 range as this is what I consciously experienced (ie. adjusting air conditioning). I still need to convert Fahrenheit to Celsius for anything outside of that range.

Also imperial sucks utterly as metric allows almost seamless exchange of mass measurements with volume for of pretty much anything in the kitchen (1g of water is roughly 1cm^3, almost everything we eat is very close in density to water).

If you use appropriate units, sure. Height of people is commonly measured in centimetres, not metres. Yes, one can easily estimate 150, 155, 160 etc. to within ten centimetres or so.

I curiously wonder on what ground the future overhauls will happen. ToE? https://en.wikipedia.org/wiki/Theory_of_everything

> a cylinder of a platinum alloy stored at the BIPM in France, will now be retired. It will be replaced by the Planck constant – the fundamental constant of quantum physics.

I thought they did that long time ago.

I wonder how much the cylinder will auction for.

At least there will be no disagreement about the shipping weight on the auction listing.

The real question is how many boxes will the fulfilment center place the kg in. If Amazon is anything to go by my money is on 3

OT, but this!

I recently ordered a picture frame from Amazon. It came in its packaging box, which was placed in a box by the manufacturer. That box was put in another box by Amazon and shrink wrapped to a large piece of cardboard, which was then put inside yet another box.

On the surface, it seems crazy, but Amazon did manage to get it to me undamaged.

My wife recently ordered five storage boxes. They arrived in two packages on the same day. One package neatly fit four of the boxes. The other package was large enough for five, and contained one storage box and a excessive amount of packing material. Not an Amazon purchase, so it must be an industry issue.

Actually, now there can be!

I have already sent an email to the Norwegian bureau of standards to inquire about buying one of their secondary kilogram standards - presumably they'll want a couple for displays and museums, but it would make for a great letter weight. (Just hoping the secondary ones are NOT also made from platinum. That is a tad too extravagant, even for a measurement nut.)

I do happen to have the previous generation time standard in my garage, though, a HP 5061A Cs clock.

> Just hoping the secondary ones are NOT also made from platinum

They are. They are made identically to the primary.

Also the tertiary ones? (I was -poorly- trying to indicate I was after a secondary /national/ standard - the ones calibrated against the national reference which is in turn calibrated against the Paris one.

Fingers crossed. :)

Considering they have measurement history on that particular object going back over a century, I guess they will continue to regularly measure it to see what happens.

If I were the president of France, I will nationalise that kilogramme.

Last I heard, the original Big K, along with (some of) the secondary copies, will not be sold. Instead, they will be observed/studied in an on-going basis, in order to better understand why their masses appear to have drifted apart over the years (which is partially the reason for this re-definition).

As I understand it the problem was not so much to find a mathematical definition of the kg based on other units but rather to find a definition suitable for experiments. If you can't practically use the definition to reproduce the prototype then it's not a very good definition indeed.

It seems that they settled on this definition because a Kibble balance[1] has shown to be precise and practical enough:

> Accuracy criteria were agreed upon in 2013 by the General Conference on Weights and Measures (CGPM) for replacing the current definition of the kilogram [...] with one based on the use of a Kibble balance. These criteria have since been met, and the definition of the kilogram and several other units will change on May 20, 2019, World Metrology Day, which celebrates the establishment of the SI, or metric system, in 1875, following the final vote by the CGPM on November 16, 2018.

[1] https://en.wikipedia.org/wiki/Kibble_balance

I did too, but apparently they only defined it for the second, meter and candela.

Are other units still tied to physical measures, or is this all of them?

The kilogram was the last unit tied to a physical object. Finally!!!

As you stroll Paris, you can still find various meter secondary standards - bolted onto public buildings to aid in commerce back in the day.

The main problem with imperial units is that it isn't a system. It's a hodgepodge of pieces of different historical systems, many of which made a lot of sense in their original context, but the context has been stripped from them and they've been mashed together with completely unrelated systems. A base-12 system would actually have some advantages, but very few of the imperial units are actually defined in terms of base-12, so it doesn't qualify.

For an engineer it's quite an anventure throughout your career discovering how many "languages" people speak: imperial, metric, IEC, ANSI, metric thread, NPT thread, all the units and industrial standards. And still foreign ISS parts mate in orbit on their first date. Or ITER parts fit toghether in plant. That's electrifying and inspiring.

The old definition of kilogram (with IPK) is no good, so it is very good that they are correcting it.

Of course you can still use imperial and other units in whatever context they are useful, and so SI units can also be used in the context where they are useful. But still I am glad they change it, because the old definition of kilogram is no good.

The Doubleclicks write a song about the IPK, the international prototype kilogram, and how it must feel about this.

https://youtu.be/VHd4HPmz5aE

Can anyone tell this poor ignoramus whether the kg is getting heavier or lighter - and how much by (approximately, I know it's not going to be an exact figure given the reason they are changing it)?

The mass of the kilogram is remaining the same. These changes don't affect the "size" of any of the units.

> "[...] the size of these units will not change (a kilogram will still be a kilogram) [...]"

> These changes don't affect the "size" of any of the units.

The size of electrical units is changing slightly. According to this BIPM document [1]: "The transition from the 1990 convention to the revised SI will result in small changes to all disseminated electrical units. For the vast majority of measurement users, no action need be taken as the volt will change by about 0.1 parts per million and the ohm will change by even less. Practitioners working at the highest level of accuracy may need to adjust the values of their standards and review their measurement uncertainty budgets".

[1] https://www.bipm.org/utils/common/pdf/SI-statement.pdf

This doesn't impact the actual weight of a kg. What this impacts is how the kg is defined, no longer does it rely on a physical kg.

It used to literally be defined as the mass of "IPK" - the international prototype kilogram. https://en.wikipedia.org/wiki/Kilogram#International_prototy...

This switch now defines it in terms of the force equivalent of the energy exerted by a single photon - if my understanding is correct.

Theoretically a more scientifically sound way of keeping 1 kg a constant permanently.

That doesn't make sense to me, the definition has changed.

The IPK was 1 kg and the copies of it were all slightly heavier or lighter, for argument let's say IPK1 was 1.1 kg and IPK2 was 0.9 kg. Now that we have a constant for the mass of 1 kg, all of those IPK's will now have a new mass relative to the new definition.

Unless the new definition was based on the current IPK and set its mass as of today as the standard, and that standard now will be unchanging?

> Unless the new definition was based on the current IPK and set its mass as of today as the standard, and that standard now will be unchanging?

Correct. The current IPK will still be 1kg to within margin of error at the time the new definition comes into effect, but any further changes to it will make it, for the first time, drift away from that value.

Ah I see, that makes sense, thanks!

Thanks. That does make sense.

It's probably better to think about the other way around. Despite heroic efforts, the "old" kilogram was getting (a tiny big) lighter every time it was handled.

The "new" kilogram will finally be a constant. To a reasonable approximation it hasn't changed at all at this moment time.

Thanks for all the comments. Very helpful.

So now packages relying on older values would have to be updated, right? In that case, wow, all those ancient - but usable FORTRAN/C code. Correct me if I am wrong.

Ideally the weight of a kilogram defined by the new definition should be identical to the weight of the old physical "the kilogram" object. The goal of this isn't to change how much a kilogram weighs, it's just to change how it's defined.

For a comparison, it used to be that we measured the speed of light as being 299,792,458 meters/second. Since then, we have defined the meter to be 1/299,792,458 of the distance that light travels in one second. An object that was 1 meter long before is still 1 meter long, but the way we communicate how long a meter is has gone from "it's how long this particular stick in France is" to a precise definition based on fundamental properties of the universe.

Welcome news.

Of course the U.S. will continue to be be the leader of the 3rd world by measuring in Royal Hangnails, Princely Bladders and Regal Farts.

I guess the next redefinition will happen if and when there's detectable drift in "fundamental" constants?

I guess the next redefinition will happen if and when there's detectable drift in "fundamental" constants?

And until then, all the metric fanbois will constantly tell you that metric is superior to imperial because its measurements are immutable. Until suddenly they are.

As opposed imperial constants? How is a foot standardized anyway? I suspect most manufactures rely on SI metrics for that.

There are no other standards. Metrology is expensive and doing it over again would offer no benefit whatsoever. All prior standards in widespread use were abandoned during the 20th century in favour of defining the relevant units in terms of SI units.

Specifically the international yard equals 0.9144 meters and the international pound equals 0.45359237 kilograms

There literally isn't another definition, in the US when you say "100 yards" the only legal meaning that has is 91.44 metres, which is whatever CGPM / BIPM says it is.

Foot is defined as 0.3048 meters, you can't get away from the SI definitions.

I've never heard anyone claim that as the reason for its superiority. Metric is superior because it makes sense as a system.

1/2 m = 50.00 cm, 1/2 ft = 6 in

1/3 m = 33.33 cm, 1/3 ft = 4 in

1/4 m = 25.00 cm, 1/4 ft = 3 in

1/6 m = 16.67 cm, 1/6 ft = 2 in

This is why imperial makes more sense to me than metric. If we had a base-12 number system, metric would be perfect, but base-10 is terrible under division. For practical divisors like these, imperial shines.

If you're doing science, metric makes more sense because units work out. But most all US science has already adopted metric.

You might be right for length, but 1st = 14lb is even less convenient than a factor of 10.

Something is 3ft x 3/8in, what area is that?

Something is 3m x 0.3cm, what area is that?

If that's one internal face of a container what width will hold a pint/litre respectively?

I won't disagree with you on this because you'll always feel more comfortable with something if you've been using your whole life. For example, I would never understand why you think 1/2ft = 6in is simpler when you have to know in advance that 1ft = 12in. It could be because I'm not used to it.

Using the metric system you'll rarely write 1/2m, as fractions are not what a person used to metric would default to. That is why 1/6m looks so weird as no one would use it like that, but if you write it 0.5m now it's obvious we are talking about 50cm, or 500mm.

BUT,

In those examples you are not using the system, you are just using one unit. If the question were, for example, what is the mass of the water contained in a 1m x 1m x 1m box, then the answer is obvious which system is by far the most sane one.

> If the question were, for example, what is the mass of the water contained in a 1m x 1m x 1m box, then the answer is obvious which system is by far the most sane one.

You're not disagreeing, the GP said

> If you're doing science, metric makes more sense because units work out. But most all US science has already adopted metric.

Your question asks for mass of a cubic meter of water, presupposing a typically scientific quantity (mass, instead of weight) and presupposing that a cubic meter (why not a cubic foot?) of water is a useful collection of water for some purpose. Fine, use metric. But imperial units as a system are made for practical everyday utility, which your example doesn't presuppose. On the other hand if we imperial users run across a situation where metric seems more useful, fortunately we can precisely convert, so it doesn't really matter.

In other places of utility (such as engineering disciplines) adopting a unit agnostic approach is the best. Some fields don't use either imperial or metric units but their own domain specific things, and software can always present units in whatever preference someone has or whatever is the most useful for the moment.

Here is a video about why imperial system is convenient for everyday practical usage: https://www.youtube.com/watch?v=r7x-RGfd0Yk

You are confused, arguments about the benefits or lack thereof of metric are based on internal consistency, not standards and metrology.

Nobody is arguing against more precise definition of standard values, which is why Imperial units these days are themselves defined in terms of SI units. So if the meter were to change, for example, so would the US foot.

The kilogram was the last one -- we're out of SI base units. This was the last one not defined based on some measurable universal constant, per https://en.wikipedia.org/wiki/SI_base_unit and https://en.wikipedia.org/wiki/Redefinition_of_SI_base_units .

The meter was originally an actual physical rod (you can see the prototype on display at the fascinating French Musée des Arts et Métiers). Now it's based on the speed of light in a vacuum.

The kilogram was a physical mass (and, yes, it was evaporating). Now it's finally defined in terms of the Planck constant, the second, and the meter.

The second was originally 1/86400th of Earth's day. Now it's based on the radiation of cesium-133 (I don't really understand how this is measured).

The ampere was originally defined based on depositing milligrams of silver from a solution of silver nitrate; it's now based on newtons and meters.

The kelvin was originally defined based on water; it's still defined based on water.

The mole hasn't really changed much? It's based on the number of atoms in a kilogram of carbon.

The candela was originally based on a literal standard amount of light emitted by candles made from dead whales; now it's based on radiation from light sources of a specific frequency and an intensity based on the watt (which relies on kilograms, meters, and seconds).

Mole was just redefined as exactly 6.02214076e23 — the number of Si-28 atoms in a perfect 1 kg sphere. This was an intentionally check against the kibble balance measurement.

More info from an older Veritasium video: https://www.youtube.com/watch?v=ZMByI4s-D-Y

Yeah, I had totally missed that a change was in the works to redefine Avogardo's number as an exact number with no uncertainty. Pretty cool.

About metric vs imperial. We all adopted 10 based numbering. That puts any system not 10 based at disadvantage.

My poor textbooks! Welp, I guess there will be some great bargains next year.

This is massive news.

I see what you did there...

The went to great lengths working on this announcement.

No they didn’t, the lengths stayed the same!

if civilization fails....how we are going to measure these things? Or then, we'll have bigger problems so who cares

On the rare chance that anyone here missed today's XKCD:

https://xkcd.com/2073/

Too bad US doesn't use them.

The US measurements system is defined in SI units. So one pound is now defined by Planck's constant.

It does actually, US measurements are legally defined in terms of metric units.

https://en.wikipedia.org/wiki/United_States_customary_units

They really should cut the middle man.

What surprised me reading that wiki page is that apparently the metric system was opposed in the US based on religious reasons. That is mind-boggling.

Is there any compelling reason why the US should switch to the metric system for daily use?

Metric is already used universally in science and engineering, which seem to be the main fields in which consistency across countries matters. I completely agree that in physics, chemistry, engineering, medicine, etc., it is important to use standard units. But what harm is it doing in practice if in everyday life, Americans say things like "I weigh 180 lbs" instead of 81 kg?

The argument that the metric system makes unit conversions easier (e.g., the fact that it's immediately obvious how many meters are in 20 km, but not how many feet are in 12 miles) is true, but not very compelling to me. I virtually never find myself wanting to do these conversions in a non-scientific or non-engineering context, and on the very rare occasions where I need to, I can always look them up on Google.

A good comparison is degrees Celsius, which are just as arbitrary/unscientific (the standard metric unit is the Kelvin). Somehow people around the world get along fine using Celsius.

> A good comparison is degrees Celsius, which are just as arbitrary/unscientific (the standard metric unit is the Kelvin).

Celsius is literally the same scale as Kelvin, just shifted so that 0c = water freezing.

Celsius is a particularly bad metric unit. It doesn't have enough units in the range most commonly encountered by humans, and it goes negative, which is also to be avoided in a good unit.

So you end up needing negatives, and decimals.

Yes, and water freezing is a totally arbitrary value.

Fahrenheit is scaled such that 0 is about the coldest it gets where I live, and 100 is about the hottest. (Very approximately, but close enough). That strikes me as a lot nicer in practice (since 99% of the time people are talking about temperature, it’s related to weather) than something based on the physical properties of a particular substance.

Also water freezing at 0 and boiling at 100 is only valid for a specific, non-metric, air pressure.

A good comparison is degrees Celsius, which are just as arbitrary/unscientific (the standard metric unit is the Kelvin). Somehow people around the world get along fine using Celsius.

You don't realize how arbitrary Fahrenheit and Celsius are until you try cooking at altitude. When I make breakfast in a particular town I frequent, it takes almost an extra minute to boil an egg.

My Jeep is a bizarre combination of metric and SAE. ISS needs to have two sets of tools[0]. NASA lost the Mars Climate Orbiter due to confusion over the units of measure[1]. Patients are given the wrong dosages[2].

It seems safe to say it's a point of ongoing friction, especially on things like international trade.

[0]: https://space.stackexchange.com/questions/12391/iss-nuts-and... [1]: https://mars.jpl.nasa.gov/msp98/news/mco991110.html [2]: https://www.chihaklaw.com/Articles/Confusion-over-metric-mea...

I already made it clear that I totally agree metric should be standard in engineering or scientific applications. I wasn’t aware that this isn’t the case in the US — thanks for the info. I believe it is at least 95% the case in the US and I think we should make every effort to get that to 100%.

I still stand by my argument that it does not matter much for everyday life.

Why have two separate sets of unit systems?

Well, the point I was arguing was "why not" have two separate systems ?

As for "why" to have them, well there isn't a good reason intrinsically -- if there were a way to magically convert the US to metric overnight, it wouldn't bother me. It just seems very unlikely and difficult in a country as huge and culturally diverse in the US. Especially since, by the standards of the rich/developed world, the US is pretty poorly educated, and also very difficult to govern (Obamacare, a law that would have seemed like a moderate reform, relatively simple to pass in any parliamentary system, is the most radical change in any area of policy enacted by the US federal congress in the last decade).

The thing a lot of people miss about the ultra-gridlocked US system is that there's a huge gulf between it being obvious to most people that "we should enact some policy" and anything actually changing. The best answer to "why doesn't the US do this or that" is often just "its political institutions can't".

Since it's so unlikely to change, and given my argument that it isn't a big deal in practice, I guess my main point is that we rationally-minded people should stop worrying/complaining about it so much.

Why should there be any separation between science and daily life?

Think about it not for the benefit of the current generation who would be forced to burden the switch, but for the next generation who could reap the benefits.

I think one issue is that by growing up with US units and then using a second system for science and engineering, it can make American students studying those topics feel like they are in an unfamiliar territory and interfere with their intuition. Most will eventually overcome this through practice and become fluent in both systems, but it's still a barrier. Science becomes a Special Discipline requiring Special Language different than what your family uses at home. Like if all science were still done in French or Latin, and you needed to study those to read a paper.

Until you have met people who grew up abroad measuring their height in cm and their weight in kg, preparing food from recipes listing ingredients in grams and mL, to whom those units are completely natural for daily life and are also the same ones they use at work when designing machines and filling test tubes, it's easy to feel that US units simply "are" the units suitable for daily life, as though that were a universal truth and not just a local cultural oddity.

Not to mention the massive net costs of having suppliers worldwide making extra sets of almost identically sized components that nonetheless aren't interoperable. Screws with 3 mm and 3.175 mm diameter, etc.

> Science becomes a Special Discipline requiring Special Language different than what your family uses at home. Like if all science were still done in French or Latin, and you needed to study those to read a paper.

You realize this is still a problem for most of the world and needing to learn English, right? :P I'm hoping we can solve this in my lifetime with everyone knowing one standard language through education as a child, but as it stands the struggle is real for many of my fellow non native English speakers.

That said I agree with you, all these differences are a pain and I'm confronted with them way too often in my daily life.

Absolutely! America is very lucky to have come out on the right side of that lottery. But then it unnecessarily goes and handicaps itself by making measurements into a foreign language.

> I'm hoping we can solve this in my lifetime with everyone knowing one standard language through education as a child

It seems like this is rapidly becoming the case in the Western world, and that that language is English.

> is that apparently the metric system was opposed in the US based on religious reasons.

As you will discover people often use religion as an excuse for things they anyway want to do. Usually they are people who only pay lip service to their religion.

Someone didn't want to use Metric. Religion doesn't actually have anything to do with it.

> That is mind-boggling.

It shouldn't be. I assume you are surprised that religion is involved in this, but actually it is not. If they were Atheist they would have the same objection, just using different words.

Basically you need to distinguish between people being people, and people acting in a certain way because of religion. This is an example of the former.

I've actually become quite fond of liquids being powers of 2 and lengths being broken fractionally. The base unit doesn't really matter (and you can always use decimal length, as is often done when building precision items).

So, for liquids,

2 tablespoon = 1 ounce 2 ounce = 1 jack 2 jack = 1 gill 2 gills = 1 cup 2 cup = 1 pint 2 pint = 1 quart 2 quart = 1 pottle ( ½ gallon) 2 pottle = 1 gallon

I find it much easier to switch units and do conversions in my head, especially when scaling recipes.

With respect to base-2 fractional length measurements, I just find it much easier to work with fractions than than with decimals. Half of ⅛ is ¹/₁₆ with next to no thought. I don't need to do division of 25 to get 12.5. It's a personal thing, but I find it nice.

Fractions are nice when the numerator is always 1. They're a pain when it isn't; sorting drill bits or buying material from McMaster Carr, you constantly have to sort out whether 17/64 is larger or smaller than 3/8, and by how much, and it becomes quite burdensome.

It's not immediate like it would be with decimals, but ⅜ -> 6/16 -> 12/32 -> 24/64 is still something I find I can do (and track) in my head with ease. Yeah, doing it repeatedly on a task would get a little tiresome. Also, who knows where the numbered and lettered series drill bits fit in without a chart.

The fractional system isn't perfect for all use cases by any means. (My understanding is that a lot of machining just deals with decimal inches directly.) I just find it convenient for many everyday tasks. I'm also weird, I guess, in that arithmetic on fractions feels easier than on decimals.

Thinking more about my original statement, a lot of it has to do with halving (e.g. finding a center) being a common operation for many tasks. It also helps that most things are sold in those fractional increments too :)

Well, you can’t suddenly replace the quarterpounder with cheese with a royale with cheese.

You would replace quarterpounder by hectogrammer. A quarter of pound is approximately a hectogram anyway.

Fun (?) anecdote - metric apparently has been used in US engineering for quite a while; a petrolhead buddy of mine was puzzled as to all the fractions used on the drawings of his (I think) Chrysler Hemi V8 from the fifties - on a hunch, we converted a few to metric. Bingo.

(Just making up a number here) 3.937" stroke? Why on Earth... Ah. 100.0mm. That's why.

Another anecdote - In structural engineering, US units are way easier to work with, and even in Canada, about 90% the buildings I work on use kips, ft, ksi, etc.

Also electronic device screen size is expressed in inches all over the world, also pipes are often inches, the same applies to nails.

In Australia, we use metric. On the odd occasion, you will find both imperial and metric depending on the application. Our wood sizes are metric, nuts and bolts can be either, nails metric, screws metric, tape measures generally have both imperial and metric, pipes are generally metric though you can get imperial if needed.

I have been using metric since the seventies. About the only things I still use imperial for are people's height and the length of fish (for undersize/oversize determination). In regards to woodworking, I much prefer metric over imperial and the millimetre over just about all other base units.

That's just my opinion.

They aren't easier to work with for any reason other than that sizes of standard components (pipes, beams, etc) are sized conveniently in US units and have US units printed on the spec sheets.

If you go overseas outside of North America, you find that the sizes of everyday objects are conveniently sized in metric, and building codes and standards and material strengths and densities are specified in SI units, and suddenly working with the metric system in those industries is easy and convenient.

Do you deal with building insulation? How would you interpret a material spec of "1 BTU ft/(in^2 hr °F)"? I had to work with these units in the US and it was not at all convenient.

I don't deal with building envelope. Its not surprising or unexpected that there are differing opinions among various professions on which set of units are more convenient.

In Canada, all our building code, material design codes, etc are in metric, and yet we are still using US units for day to day design.

What lengths and widths of wood can you buy from the lumberyard?

What is the common width and thickness of drywall sheet you can buy and the hardware store? What door sizes are available? What size of screws are cheaply available in Canada?

I think these factors are far more likely to affect what unit of measure is commonly used in construction, rather than any intrinsic merit of the measurement system. If you were shopping at a Japanese or German hardware store, you'd probably suddenly find all of those 12 foot dimensions quite frustrating and not be at all surprised to find the hard-hat-wearing locals happily using the metric system for the same tasks.

Anyone who is doing real work in the US uses SI units. The only case where you're using "feet", "miles", "pounds", etc. is in everyday language.

NASA and NOAA scientists and engineers still use customary units.

The US didn't adopt the metric system because it was considered blasphemous since the French used it. I'm not joking. We got screwed by a bunch of demagogues.

The US officially adopted the metric system in 1975 with the Metric Conversion Act.

The act does not require the US to use metric in any capacity. It is optional. If it did kids would not be taught using the imperial system.

The US uses customary measures. Imperial is the old UK system. It has some important differences like the size of a gallon - and perhaps most importantly if you like beer: the size of a pint.

There are a lot of situations in the US where using dual measurements, or just using metric is required, like food labeling. Using customary units is optional in many cases

Moreover the US signed the Convention du mètre [0] in 1878. By law all US customary units are based on SI units since 1883 [1]

[0] https://en.wikipedia.org/wiki/Metre_Convention [1] https://en.wikipedia.org/wiki/Mendenhall_Order

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