Units - the Measure of our Lives

by Matt Bryan

Units of all sorts dictate our everyday lives, whether it be how far we commute to work, whether we decide to put on a coat having looked at the temperature, or whether we have another helping of lasagne. And it has been that way for centuries - units of measurement were some of the earliest tools invented by mankind, they standardised trade throughout the ancient world, helped keep track of vast empires and aided the everyman in their trade. The world has always been a veritable sea of different units, but in the last few centuries, attempts for international standardisation have been relatively successful. The Système International d’unités or SI is the most modern form of the metric system developed in France, first beloved by scientists and then the world over, and it’s been that way since at least 1960. Well at least for most of the world.

The natural exception to this rule is the US, but I’ll save the jokes about how they measure speed in hamburger radii-per-fortnight or pressure in poundals-per-township (surprisingly both ‘valid’). The issue could be said to be one of national pride, the US having extensively developed their own imperial-style system post American Revolution as part of Jefferson’s policy, but it’s more modern than that. Most of the world moved to teaching metric in the 60s/70s, but Americans didn’t see the need to do so - that their system was perfectly fine. Yes, imperial measures do function day to day, but when you get to the point that your top scientists, those you praised as national heroes in the late 60s, reject your own units as to avoid ridicule from their international colleagues, then they might be flawed.

I suppose the same is true to a lesser degree in the UK, but many probably see the way our signs are in miles and heights are in feet as a charmingly quaint callback to a bygone era. But ask the same people how many yards are in a mile and only a lonely few will answer (it’s 1760). Using miles works on the most part, as the conversion from kilometres to miles is about 1.6 times, and a yard is pretty close to a metre, but if you are doing any sort of measure where these are critical, then you would go straight to SI. The beauty of metric is that it is based on base 10 or the decimal numerical system, the very same we humans use. Just as computers at a low level run on binary, it’s ones and zeros that make sense to them. Imperial systems run on a range of bases; sometimes there are 16 ounces in a pound, eight pints in a gallon, but 231 cubic inches in a US gallon. It requires significantly more memory recall and makes switching between units within the same system a complete nightmare.

As good as it is, the metric system doesn’t have a perfect record; rather the current SI system is an amalgamation of ancient units like the second (now with a highly defined definition related to electron transitions in caesium-133), and more modern inventions like the kilogram (firstly based off a physical artefact and now using an precise, equivalent photon mass). For a few years during the chaos of the French Revolution, the days had 10 hours, each with 100 minutes and each of those with 100 seconds. Needless to say this never caught on, and neither did the Republic’s calendar of 12 months, each with 30 days and the extra few left over being holidays. But in this case, the Revolutionary metric system sought to change something that wasn’t crucial to scientists or professionals who relied on time - they were only interested in the change in time, or period, between events, so changing the whole calendar upon which Western tradition was based seemed a little extreme.

So, in the present day, everything just about works - except when a few units make little sense. Take fuel consumption for instance. If you are British, you likely measure this in miles-per-gallon; this gives sensible numbers which are easy to understand, and are almost always in the range of 0 to 100. But this is an inverse relationship, meaning that the higher your ‘mpg’, the less fuel your car uses per unit distance. In most of Europe however, litres-per-100-kilometres is used, which is not an inverse relationship; ie. the higher your L/100km, the closer your car is to a petrol bonfire than an efficient little engine. So when it comes to ‘mpg’, the relationship between this figure and the actual consumption of the car is not simple. For example, 40mpg is around 7L/100km, but that makes 20mpg about 14L/100km. Most people might not envision such a difference between 20 and 40 mpg, but there certainly is one. Perhaps the worst of all is how pointless using gallons is: miles makes sense for the UK, but ‘ye olde’ gallons? Petrol pumps read in litres and have done for decades, so to convert you have to remember that it’s about 4.5 litres to the gallon, but it’s actually 4.54609 to be exact so the figure loses all sense of meaning. And then horsepower is different to PS which is different to imperial-horsepower and it’s all just such a mess.

But there are still two even more annoying relics that fill me with rage whenever I see them - the BTU and cups. The British Thermal Unit, an antiquated unit of ‘heat’ or energy, is a menace for a number of reasons: it firstly has the worst definition imaginable. “The energy required to raise an avoirdupois pound of water by one degree Fahrenheit at a pressure of one atmosphere”. The avoirdupois pound was introduced in the 13^th Century as 6992 grains, so it was hardly even exact nearly a thousand years ago. Then it uses Fahrenheit, a temperature scale that uses brine as a reference point and has changed definition countless times. And an atmosphere until relatively recently didn’t have a proper definition, just ‘the pressure exerted by 760mm of mercury at 32^oF’. Yet this unit is still used throughout the American energy sector, and its name gives us Brits a bad reputation. A BTU is also about 1055 joules, depending on who you ask - if it’s a Canadian, it’s 1054.68, an American, it’s 1054.80 or a ‘scientist’ and it’s thermodynamically defined as 1054.3504 J.

Nonetheless, I saved the worst for last - cups. How can a unit be based off of a drinking vessel that has been manufactured for centuries in all shapes and sizes? How can one choose the cup which defines all cups, by which, all other cups shall be judged? It’s ludicrous. But none of these questions matter because the US government, by law, decided the cup was 240mL, but then the Brits came along and said it was half a pint, and then the metric system came to the conclusion that it was 250mL, but then again the custom of the US thought it was traditionally more like 8 and a third fluid ounces, or exactly 236.5882365mL. 

In short, there are at least as many definitions for the cup as the number you probably have in your household. You might appreciate that they are widely used in cooking, so the exact nature of the cup is used as more of a sort of ‘about so much’ when it comes to volume. But pretty much everyone can understand the litre - it’s a kilogram of water and a mL scale appears on any measuring apparatus I can imagine. Yet there’s still some sort of use for a ‘cup’, and a heaped tablespoon when none of those words mean anything empirically. Maybe if I was a better cook, I’d have a sort of indescribable intuition for these sorts of quantities, but until then, I’d rather complain about it - anyways, it gives something to blame the taste of my dishes on.