That last one is what I have the biggest problem with. When you are doing anything with derived units, 'kilo' suddenly disappears.
Having decimal numbers, it’s the best solution. Otherwise you’re bound to make mistakes scaling things up or down.
> a liter is not a cubic meter
Well, it’s a dm^3, close enough ;) Conversion is trivial, 1 m^3 is 1000 l. A cubic metre is a bit large for everyday use, but it makes sense e.g. when measuring water consumption or larger volumes. The litre also had the advantage of being close to 2 pints, so it already made sense as a unit when it was introduced. Contrary to hours with 100s.
> 'kilogram' is the base unit, not 'gram'
Yeah, this one is perplexing. It’s an annoying inconsistency on an otherwise beautifully regular system.
Anyway, the point is the inconsistency in the system due to the kilogram being the base unit. So derived units are defined in terms of kilogram rather than gram. Say, the unit of force, Newton (N), is defined as kgm/s^2 and not gm/s^2). Or pressure, Pascal (Pa) which is N/m^2 which inherits N being defined in terms of the kilogram). And so on. Anyway, an annoying inconsistency maybe but doesn't really affect usage of the system once you get used to it.
Considering today we set the kilogram by fixing the Planck constant and deriving it from there, we can just divide each side of the definition by 1000 and use that as a base unit. Using kg as the base unit is completely arbitrary, as we can derive each unit of weight directly from the meter and the second, not from the base unit.
Changing it to ~1,000 times what it used to be, or giving it a new name, would force people to realign.
There's reason many people still prefer customary and imperial units, and it's not just bigotry and nationalism (even if they play a part in that preference).
As the name kilogram implies, gram is actually the unit here. But it was derived from the mass of a standard 1 kg chunk of metal that lives in a museum somewhere near Paris. This is the literal base unit of mass (at least historically, the definition has since been redefined using the Planck constant). A 1 gram chunk would have been tiny and be tedious to work with doing e.g. experiments with gravity.
They also have the original prototype meter in the form of a length of platinum-iridium alloy bar. And because the specific reference object for mass weighs 1kg instead of 1g, it means 1kg is the base unit in SI.
But quite obvious in the system of measurements, the gram is the logical unit here that you augment with prefixes and people commonly handle a lot of mass quantities that are in the order of grams rather than kg.
Derivations are simple. Simply apply powers of ten and their commonly used prefixes (kilo, milli, mega, micro etc.). The base unit is something physical that you can point at as the base unit. Or at least historically that was the intention.
There's also convenience. A 1l of water is about 1kg and a volume of 10x10x10cm. or 1 dm3. That's not accidental but intentional. It makes it easy to work with volumes and masses for people. Never mind that a liter of water isn't exactly a kg (because water purity, temperature, and a few other things).
Every formula using SI will expect mass in kg and you will be off a factor of 1000 if you use gram as the base unit. Same with derivative units like the newton which all use mass in kg for conversion.
EDIT: Yes, yes, SI defines the kg and then the g by reference to kg, but so what, notionally it's still the gram that's the base unit.
This one isn't metric's fault to be fair. That's just what you get for inventing numbers before inventing math.
Makes me wonder what would have happened if 'French numbers' in base 12, 36 or 60 were introduced at the same time.
People got used to working in octal.or hexadecimal in the past for computers, doesn't seem like it would have been as big of a change as you think.
Irrelevant with a decimal system.
You're making an argument from familiarity. Yes, a 12-base system using fractions works very neatly in a small human-sized domain, but it disintegrates into complete uselessness outside that domain. That's why you get ridiculousness as things being 13/64th of an inch, or that there's 63360 inches in a mile. It's unworkable for very large distances and very small distances. With a metre and standard prefixes, you don't need any conversion factors, and you can represent any distance at any scale with a single unit.
Quick, what's 11/64" + 3/8"?
Quick, which weight is bigger: 0.6lbs or 10oz?
You can use hexadecimal numbers if you wish. "He's B6 cm tall."
I have found this, which seems neat: https://en.wikipedia.org/wiki/Bibi-binary
So he's ki-ba cm tall.
Such fractions are very rarely used, you're more likely to use mils (1/1000 of an inch) at that scale.
> or that there's 63360 inches in a mile.
Likewise, something that will probably never come up in your life. Inches/feet/yards and miles just remain separate things, never mixed.
> With a metre and standard prefixes, you don't need any conversion factors, and you can represent any distance at any scale with a single unit.
There's no intuition for them. Knowing what a meter is does not help with getting a feel for a kilometer. They might as well be as separate as feet and miles at that scale.
> Quick, what's 11/64" + 3/8"?
That one's not even hard, it's just a fraction. 35/64"
> Quick, which weight is bigger: 0.6lbs or 10oz?
Another arbitrary problem that will probably never come up, but to entertain you: since 0.5 lbs is 8oz, adding 1.6oz to that (another tenth of a lbs) results in 9.6oz. 10oz is bigger than 0.6 lbs. Not hard, but at least mildly harder than the first question.
None of this really had to do with the convenience highlighted initially: 12 inches in a foot and 3 feet in a yard make extremely convenient divisible factors. You can trivially divide things by 2, 3, 4, and 6 and keep with whole integer values. The same definitely cannot be said of metric.
How tall are you, maybe 70 inches? Or 5⅚ft?
178cm or 1.78m are so obviously equivalent it doesn't matter which is used.
> 12 inches in a foot and 3 feet in a yard make extremely convenient divisible factors.
This requires you to start with 12 inches. If you're making a cupboard to fit in an 18¾" (476mm) space, it's no use, or is only randomly useful.
If you can choose, then you can just as easily start with 36cm. For example, European kitchens are designed around a 300mm base size.
Are you purposely doing this? That is obviously not what I meant. Nobody says "3 miles, 500 feet", they say "3.1 miles". Effectively two systems of distance measurement: inches/feet/yards (near scale), and miles (distant scale).
"5 feet 10 inches" is completely normal and fine.
> This requires you to start with 12 inches. If you're making a cupboard to fit in an 18¾" (476mm) space, it's no use, or is only randomly useful.
So you cut the cupboard to fit a 18¾" space, no big deal. Same as anything else, and just as random as 476mm.
Typically they come in (integer!) 12-inch, 24-inch, 36-inch, or 48-inch variants.
Fucking bushels, man.
Nobody cares how many inches are in a mile. It doesn’t matter.
> Quick, what's 11/64" + 3/8"?
35/64. Was that supposed to be hard? Common denominators are elementary school level arithmetic.
> Quick, which weight is bigger: 0.6lbs or 10oz?
10oz. 10/16 is 5/8 which is .625.
I agree that metric is easier for people who don’t have a grasp of fifth grade arithmetic.
Highly relevant if you are using T-squares, compasses, and dividing calipers.
So instead of buying 100cm planks, buy 120cm planks?
Which is why the imperial lovers all cry out about their fractions not "working" in metric. Yes, exactly, that is the point. They don't understand that they're reaching for a tool they shouldn't be reaching for, and then they blame the unit system for it.
Base 6 would've been the real deal.
The _other_ reason to use a measurement system is for doing _science_, and for that, having everything in base ten makes things _immensely_ easier, especially if you're working the math out by hand
Again, this is just familiarity. You think it's super neat that you can divide a cup of whatever by 2 or 3 or 4, but if I tell you to divide it by 5, you're gonna deflect and ask me "who does that?!?"
Imperial works neatly for a small domain of problems, and is useless outside that domain.
Metric is less neat in that small domain, but works equally well everywhere.
Firstly, we can divide a cup by 2, 3, and 4 in the kitchen because those are common measuring-cup sizes. Nobody is prevented from using a fractional size: if I divide a cup by 5 then I have 1/5th of a cup, nothing more and nothing less.
While 1/4th of a cup is 2 oz, and 1/3rd of a cup is 16 teaspoons, 1/5th of a cup doesn't divide evenly into a smaller unit and that's why "we don't do it", but there is nothing to stop the chef from using 9 teaspoons. [Or he can instinctively go up to 45mL on his graduated measuring cup, which almost always has both systems on it!] Teaspoons, tablespoons, ounces, cups, quarts and gallons are all inter-related multiples, and once you internalize it, you can convert like a boss.
While I'm sure it's lovely that metric measures divide by 2 and 5, that's all they divide by, so in terms of divisors, you've lost 3, 4, 6, 8...
So if it really is about dividing things usefully without resorting to fractions, then using a system that is nothing but multiples of 10 is a handicap, when we've had systems with lovely 12s and 16s with many different options for dividing them up.
But the metric people can simply chop up the measures even more finely and claim victory. For example, currency: it was in multiples of 16 or 8 which allowed for limited permutations. Decimalization chopped it into pennies, and we find 100 gradations in every pound sterling. All that did is make base-10 math easier for bean counters, and confuse people on the streets with a mystifying array of coinage. [Mental math indicates that it must increase the volume of coins per average transaction, as well.]
If a basic customary unit of length is an inch, many people can put two fingers together and estimate that on the human scale. But who can estimate or eyeball a millimeter?
Oh, and, have you ever found a nice British recipe in metric, shopped at your American grocery store, and prepared that in your American kitchen with your Fahrenheit range? You will eventually want to tip it all in the rubbish bin. Adam Ragusea suggests as much: https://youtu.be/TE8xg3d8dBg?si=SD8wLxD6ib6InLX4
"It's super easy if you're familiar with it!"
Yes, that is exactly the problem that you are unable to see.
If you'd grown with a metric system you could eyeball a centimeter with ease. Also comparing orders of magnitude different measures for estimation isn't fair, how precise would be your guess of a barleycorn?
And the division issue is almost trivial in my view; you can just take 120 cm or 12 gram quantity. You don't magically lose the ability to divide things by other than 10 or 5 or 2 when using metric. Its not like decimal fractions disappear in imperial systems either. The metric system is there for making it easy to scale things between orders of magnitude and have sane conversions between units.
Probably most people in the world. I can for sure do it. It's trivial if you grew up with the system.