Off topic Question.
What is the story behind Celsius and Fahrenheit? What US continue to use F when the rest of the world is now on C?
What is the story behind Celsius and Fahrenheit? What US continue to use F when the rest of the world is now on C?
The United States is sentimentally attached to its pre-SI units more than they care about international inter-operability – so they continue to endure the ongoing cost of juggling a separate system of units while also using SI units in most science and some engineering work.
It's all quite confusing when you explain it, but pretty natural when you live there
My old flat had a faucet that was a pain to update to a mixing tap because the hot water used inch threads and the cold used metric....
Since everything is fractions you don’t get irrational numbers and calculations are super easy even without calculators case and point say you need to square a measurement squaring 3/16th of an inch is something any fifth grader can do in their head or simply look it up in an easy table. Squaring 4.7625mm on the other hand requires a calculator and since you get an irrational number you can’t easily accurately measure it with common tools in the real world.
What stops one from using 3/16th of a meter? (I admit I rarely see SI units with fractions, but if one finds them so useful, why not? Personally I prefer non-fractions by the way, it's much easier to rank and compare numbers in your head if they're all given as real numbers. E.g. can you tell quickly if 5/17 is bigger or smaller than 8/30?)
And how will you square 2.829 inch? Not everything you measure will happen to be some perfect fraction
For the other metric units, such as meters and grams, the new units had a clear advantage over the old: decimal based subunits.
That was an advantage that you could not simply add on to your existing units without making a total mess of things.
This does not apply to temperature, because we very rarely use subunits with temperature.
Furthermore, the other base units are frequently used together in very commonly used derived units. For example, force is length x mass / time^2, pressure is mass / length / time^2, and energy is mass x length^2 / time^2. Those are all important enough that they have their own names.
There are no commonly used named derived units that are based on temperature (and I can't actually offhand think of any named derived units based on temperature).
In short, a government can make a pretty good case to its citizens to switch to meters and grams, despite the costs of dealing with that obsoleting a whole bunch of existing rulers, scales, and written records, because it is actually a better system.
But as far as I can tell, meter+gram+F would work as well as meter+gram+C, so it is hard to make a good, let alone compelling, case to your citizens that it is better. All they've got is "everyone else is doing it".
For meters and grams, "everyone else is doing it" might be good enough, even if meters and grams were not actually better than the old system, because of international trade.
People choose dimensions and weights of goods to come out nicely in the units they use, and they want to buy goods with nice dimensions and weights, so if you are trading internationally in goods, you have to deal with length and mass units of your trading partners.
Length and mass cross borders in trade.
For temperature, that is generally not the case. If I'm importing stuff from, say, France to the US, for almost all goods it does not make one bit of difference if France and the US use different temperature units.
Temperature does not cross borders in trade.
Everything is essentially always divided by two 1 inch, 1/2 inch, 1/4 inch etc, or by 1000 when very fine precision is required.
You never get numbers that are hard to add up, divide or multiply when this especially comes into play when calculating derived units like PSI, clamping torque etc.
And more importantly it makes calculating squares which are often used quite easy it’s much easier to square 3/16th of an inch than 4.7625.... mm
Metric only really allows for easy conversion between magnitude of scale but when it comes to other calculations you get numbers which are hard to accurately calculate in your head and irrational numbers much more often than when using imperial units.
And irrational numbers can’t be measured. It’s very easy to make a measurement tape that does 1/16th of an inch increments and measuring 3/16th of an inch is a breeze measuring 4.76251784744823823... mm on the other hand is eyeballing it.
If you're dealing with something that's already constructed, then you won't get a measure like 4.7625mm. You might measure 4mm or 5mm. (Otherwise I may as well say that 4.8mm ~= 7/37in and ask you to add that to 3/16in.)
0 is roughly the temperature on the coldest series of days in most of the continental United States and Europe, and 100 is roughly the hottest.
Celsius is great for measuring water while cooking. 0 is freezing (at sea level, assuming a normal room temperature) and 100 is boiling (again, with caveats).
The metric system has everything evolving around a cubic meter of water, so Celsius is easy to grok, and feels logical.
But, having lived in the U.S. and Europe roughly an equal amount of time, Fahrenheit is much much more accurate to estimate outdoor temperature with.
And as it turns out, that's what most people are doing.
Cute asides: The meter is based on a miscalculation of the distance between the equator and North pole. The SI couldn't find anything absolute that actually matched their arbitrary size, so made it dependant on a bar in the SI building, and then realized the bar is changing sizes with time! (This is finally being rectified with some atomic measure.)
On the other hand, my sixth grade teacher taught us that 0 is the freezing point of beer, and 100 is the body temperature of a cow. So, the theory is that some drunk scientists thought a cow had fever..
Which most people are you talking about?
I don’t know anyone outside the US and occasionally the UK who uses Fahrenheit. That’s not “most people”.
Actually the definition has gone through a number of rounds of increasing precision. It did have an atomic definition for a period of time, but now it's based on the speed of light. (IE the distance light travels in a vacuum in 1/299792458 of a second.) Too bad we didn't know the exact speed of light before coming up with the definition, or we could have a nice round 300,000,000 m/s!
Actually, if there wasn't so much politics (and fake science) involved, there are plenty of things they could have used from the get-go that would have been nice and round.
The "nice round" figure that you offer from the speed of light, and suggest that they would have used had they known it then, is not nice and round and it is not related (and therefore would not have been used).
(1cm = 2.54in IIRC)
1 inch = 2.54cm
Imagine if 1 inch = 2.56 cm
My point about the speed of light was that if we were coming up with a unit of measure now, we would not arbitrarily base it on the distance from the equator to the pole, which is by nature imprecise, but rather on the speed of light, since that is the most fundamental and precise reference we have. And if we were basing it on the speed of light, we would pick a round number, because there is one available that results in a meter of useful length. (By chance, very close to the actual meter.)
Of what use are the smaller steps with Fahrenheit ?
I can not tell if it is 30 or 31 °C outside.
Most thermostats I've seen allow changes of 0.5 degrees C. So it seems that the thermostat manufacturers feel that the majority of users can tell a difference.
And sometimes 1 degree C delta is too much for me in a room (e.g. 21.0 is comfortable, 22.0 is not, 21.5 is just right). So it's obviously a personal preference, but at least for me, I can tell a difference between 0.5 degrees C.
And thus for my use case, whole integers in F is a slightly superior user experience since it avoid fractions.
This argument to me makes no sense: most of the human beings don't live either in the continental US or in Europe :)
0 Celsius to everybody means rain would ideally turn into snow, which makes it great for "measuring weather". And it is useful for agriculture too.
The same happens with voltages, what side of the road you drive on and the use of imperial for building materials as well as telco standards.
Island nations and very large territories are the ones that exhibit these properties because they can.
What is worse is that as soon as the US invades some territory they push their standards.
The funny thing is that the military usually gets it right because they only care about two things: accuracy and efficiency, there is no consideration for costs to switch or legal hassles, they just choose what works best.
I would have guessed it is arbitrary, but you may know something I don't. So I'm curious to learn about it.
One Nautical Mile is roughly 1852 metres, so 1 kt is roughly 2 km/hr. More accurately, 1 m/s is very close to 2 kts.
Fahrenheit gives more granularity without the need for a decimal when thinking about temperatures most people would experience on a daily basis.
A normal spring/early summer might have temperatures ranging from 4-38°C or 40-100°F, Fahrenheit gives 60 distinct steps where Celsius provides only 34.
Your used to it, and the explanation is an invented justification.
I lived all my life in metric countries, and have never heard anyone use a decimal to describe the weather, except for a record (47.6°C or whatever it is).
To me, this is a pretty clear indication that people can feel the difference in half degrees Celsius (otherwise, why would the manufacturer bother with it?). And because of that, Fahrenheit is better for human-scale temperatures, as only two significant digits are required instead of three.
That doesn't necessarily mean that they can distinguish two identical rooms with 0.5°C temperature difference.
I personally find Celsius more intuitive when discussing outdoor/environment temperatures, because that's what I grew up with.
Seriously, don't try to invent reasons why Fahrenheit might be more intuitive than Celsius, it's not. Neither is superior, no matter who you ask the more "intuitive" will always be the one a person grew up with.
I just wish the whole world would use a single scale because that's less confusing. And here the argument is on the Celsius side because only a small minority of people in the world (<5%) use Fahrenheit.
Units of length on the order of a finger-width (inch), foot-length, or stride or arms-width (meter), or area that could be plowed in one day (acre). You don't need special calibrated tools to measure/estimate these.
Units of volume are based on successive halvings (1/2, 1/4, 1/8, etc.) because all you need is two identical cups to split a liquid to be the same level in each--works for non-liquid volumes too, if you measure them by submersing in equal volumes of liquid.
The unit of mass -- pound -- is similarly split into 16 ounces because the pound originated as a measurement for silver, and a simple balance could be used to split 1 lb silver into 8 oz, 4 oz, 2 oz, 1 oz, or smaller, and then be combined to make change.
Units of temperature have integer gradations approximately equal to what sensitive skin of the human body can discern in the atmosphere--I can feel the difference between 70 and 71, but not 70.0 and 70.5--and a nice even value for the normal temperature of the human body (above 100F, you have a fever). Arguably the boiling point of water is more important these days, but only since the rise of steam power and other industrial things that get very hot.
What system would I rather use, if I were hypothetically not already accustomed to one? Well imperial has clearly better optimized user experience, even if some parts have aged with technological change less well than others. It co-evolved with pre-industrial human societies but is still well matched to the day to day environment we find ourselves in, even today, in the produce aisle of a grocery store, in the kitchen, in estimating the weight or size of things we might pick up, etc. Example: when I open a recipe and it says "3 cups of flour and 2 tablespoons of baking soda, 1 teaspoon of salt" then I don't need any special measuring cups or scales to make this recipe--I can make do with stuff lying about the kitchen--it's in the names! Take something that looks like a average-sized drinking cup or mug and fill it with flour three times, take an eating spoon and fill it twice with baking soda, and take a drink-mixing spoon and make one scoop of salt. Alternatively how am I supposed to interpret 0.75 kg flour, 30 mL baking soda, and 5 g salt? Either I've cooked and measured enough to have an intuition for such things, or I'd better have calibrated tools available.
What do you get in return for using the not-so-human-scale SI units? Nice powers of 10? No one was ever stopping you from talking about mega-pounds or micro-inches, so long as you're consistent on lbs vs oz and ft vs in. Imperial units aren't any different in this regard from saying "2 hours" in an SI context and people knowing to multiply by 3600s/hr to get the official unit
At the end of the day I prefer SI for the same reason I prefer English--as a global standard because it is the standard, even though it is actually pretty terrible. It's a bit like Qwerty vs Dvorak/Colemak/Workman, except the decision isn't a personal choice. I do wish the French had decided things differently some 225 years ago though.
[0] I'm struggling to remember what they were I thought I remembered cubits but I'm not sure why you would find those on a tape in the 1940's. Anyway, never let the truth get in the way of a good story.
I think the parent is right that it has mostly to do with what you are used to.
Your volume measure has no convenient relation to a length³ measure. I can tell you the volume of this room in litres very easily given the dimensions, but "1 cubic foot = 576/77 US fluid gallons".
"There is not a single agreed-upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C (99.5 and 100.9 °F)" (Wikipedia.)
You've made a false equivalence of your recipe. We can write "2dL flour" and so on, although flour in particular can have varying densities, so results are much more consistent when weighing. My British grandmother's recipes say things like "8oz flour" and were always weighed.
I can do halving and so on with metric or arbitrary tools (this glass/stick) when necessary, and can expect to have appropriate measuring tools available when I need them. So, since I'm not living in the 16th century, I don't see any benefit to the old units.
A difference smaller than 2C is usually negligible, unless you're close to the freezing point. So even Celsius is "overaccurate"
The intuitiveness of a measuring system is mostly people growing accustomed to it. If you've lived in a child place you probably couldn't tell the difference between 30C and 40C
Outside temperatures vary by a lot more than 1 degree (the difference between precision and accuracy?)
The place I have seen where Fahrenheit makes sense is for human temperatures - what temperature is a high fever?
I have never seen an aircon unit with half-degree Celcius settings, except in some cars which to me seems to be an anti-feature.
They are both hard words to spell, but Celsius is shorter, so a big win for °C there!
This clearly wasn't always the case, but the polarisation of American politics continues to increase.
It's similar in Britain, except there was more progress there before Conservative people took it as an attack on tradition and made it political, and more pressure (legal and practical) to conform with the rest of Europe.
The only meyric measurements in the US are in science.
And there's like 4 different units for pressure IIRC.
I think that is what I said when I said all research done in universities, the military, NASA, etc. is done in metric.
The point I was trying to make is that the US is more metric than most people think about and has nothing to do with "conservatives". The parts for my car are in metric, the wine I buy is in 750 ml bottles, medicine I take is in metric, 2 liter bottles of cola, illicit drugs (grams or kilos although I don't take that!), etc.
Yes there are different units for pressure but the one used by the university I work at is metric.