The Rod Delusion

Every so often, in Internet discussion forums, national newspapers, or real life (no link for this one, sorry), I have an argument with someone who is against the Metric system. These are people who I do not suffer gladly. The worst of them are those idiotic “Metric martyrs” who point blank refused to use Metric units and then complained when they had their little shops shut down, as if insisting on only using Imperial units was somehow different to insisting on only accepting Canadian dollars and only speaking Esperanto. The fact is that nobody was, then, now, or ever, trying to stop them using whatever screwy units they please. The rules simply state that metric conversions must be printed so that everyone knows what’s what.

To help with these arguments, mostly as a resource for myself, I shall now compile as full a list as I can of flaws with the Imperial and US customary measurement systems. It won’t be a full list, because listing all of them would be like spotting errors in The Core, a task I have previously likened to counting raindrops, but here goes anyway. Feel free to add more to the comments section.

When Is A Pint Not A Pint?

Answer: when it’s in America. Because an Imperial pint is roughly (but of course, not exactly, because that would be too simple) 20% bigger than an American one. Americans call their units “Standard”. Interesting. This means, of course, that if you read the word “pint” in, say, a recipe, there’s really no way to be sure what that means. From here on in I shall switch back and forth between US and Imperial units with no warning because that’s what real life does. In my experience, most Americans are unaware of the difference between the two systems anyway (which of course exacerbates this problem enormously). Metric does not suffer from this problem.

How Long Is A Piece Of String?

All rods, poles, perches, cables, hands and feet are the same length. All chains are the same length. They all comprise 100 links, and they’re all exactly 100 feet long…

Who’s Asking?

…unless, of course, you work as a surveyor, in which case a chain is sill 100 links, only now it measures 792 inches as opposed to 1200. I don’t give the conversion in feet because a surveyor’s foot is very slightly longer than a standard foot. This makes show shopping difficult. Also, of course, if you’re a sailor then a mile is a different length than if you are a motorist. This does not happen in Metric.

Non-integer Conversion Units

This, of course, means that to convert (surveyors’) links into inches, the conversion factor is 7.92 inches to a link. There are two-and-two-seventy-fifths yards in a fathom. There are five-and-a-half yards in a rod, which is the same as sixteen-and-a-half feet. These aren’t extreme examples: these are typical. Imperial was formed largely from feet and inches, but people made new units by multiplying them by whatever seemed convenient and then made yet more by dividing those down. Once you start manipulating them in any serious way you end up with ludicrous conversion factors running to many, many digits. All Metric conversion factors are not only integers, they are powers of ten. All of them. It is impossible to manipulate Metric units and end up with any conversion factor which isn’t just a one, some noughts, and maybe a decimal point.

What’s In A Name?

As well as having names with more than one unit attached, Imperial and US measures also have units with multiple names: as mentioned before, a link is (sometimes) equal to a foot, but a rod is the same as a pole and they’re both the same as a perch. Not only that, but the names bear no apparent relation to the sizes of the objects involved: a foot is the size of three hands, and a link in a chain is the size of a football. Imperial handcuffs must look decidedly strange. Not only that, but a hundredweight is not 100 of anything. It is 112 pounds. Imperial advocates will tell you that this factorises easily. Well yeah, but it divides by seven. What use is that to anyone?

A Bit Much…

Imperial has far, far too many units for any human to remember. To use Metric for almost any purpose, you need to remember maybe four units and three prefixes. Imperial has a dozen weights, two dozen lengths, a handful of areas, and some volumes, and there’s no way to work out what any of them mean. When you have to look up what the units mean that is inconvenient. When, having done so, you discover that they are identical to units you did know, that’s just adding insult.

…But Still Not Enough

Despite its surfeit of units for everyday metrics like length, Imperial is shockingly bad at (for example) force, resorting to multiplying the pound (which has suddenly been defined to be a unit of mass rather than weight) by g. Metric has a dedicated unit for this, the Newton, which is readily converted into seconds, metres and kilograms. The “poundal”, the rather silly Imperial unit of force, is equal to 32-and-a-bit pound feet per second squared. What use is that? The equivalent conversion factor in Metric is simply 1. It’s convenient for discussion of forces, and it follows the Imperial rule of keeping to units people can easily judge, but you should never have a conversion factor like 32.1740486.

There’s also no Imperial unit small enough to measure atoms or large enough to measure galaxies. Metric, with its cunning use of log scales, has several units smaller than an electron, and another equal to about a hundredth of the width of the universe. The Imperial system simply doesn’t scale.

Bad Science

The upshot of this is that you simply can’t do science in Imperial units. It’s just not practical. It’s possible, of course, but it would be a fantastically stupid thing to do. For any halfway complex task, it would be quicker to learn Metric and use that than to use the Imperial system you already know. Partly because, as mentioned, the units are ambiguous. They are designed only for use by chefs on Earth. Chefs on Earth really need no distinction between mass and force, and so they didn’t make one. When you do need one and find it isn’t there, problems arise.

The Long And Short Of It

I appreciate there are sound historical reasons why “pound” abbreviates to “lb”, but I’m unaware of any such excuse for spelling “ounce” with a ‘z’ or those downright fucking bizarre symbols used in Apothecaries’ weights. And whatever the reasons, it’s still a whole bunch of other asystematic stuff that needs learning.

Update (24082007): When Is A Cup Not A Cup?

Answer: when it’s a unit of measurement. If a recipe, say, is translated by a computer or a person unfamiliar with the system, the unit names will be turned into the objects they’re named for. And who knows what size cup the reader might have? Using names of objects for units will lead to confusion. This problem doesn’t happen with Metric. Similarly, if you’re not translating them, a reader may not know that a “cup” can also be a unit. They might think it refers to, say, a cup. And they might have massive cups. There’s no danger of that with a “litre”.

In short, there is exactly one valid reason not to switch to Metric: the switchover itself would be expensive and difficult. But if anyone tries defending the Imperial or US systems in and of themselves, then they are just being obstinate and narrow-minded. The most common attempt to defend the system goes like this: “Metric makes you stupid because you never learn how to divide by twelve and stuff.” This is rather silly. There are two possible scenarios here:

1. There exists a large number of things for which division by numbers other than powers of ten is a useful skill. Therefore, removing one of them should make no material difference.
2. There does not exist a large number of things for which division by numbers other than powers of ten is a useful skill. Therefore, that skill is largely pointless and we may as well save ourselves the bother of developing it by using the simpler system.

Neither of those scenarios offers a good reason to stick with Imperial. Because there isn’t one. Sometimes people claim that Imperial units are more natural. This is true up to a point. Feet and inches are quite handy lengths for rough working. Luckily, they both convert fairly readily into Metric – there are about three feet in a metre and two inches is 5cm. The rest of the units are really only convenient because you’re used to them, or because there are simply so many units it’s hard to imagine how there could fail to be one the length you’re looking for. Well, unless you’re not human.