A Sensible Choice of Units

I am a scientist, or at least I spend so much time pretending to be one that I may as well be one. One of my pet peeves are units, those things that go on the end of numbers and give them meaning, well only some units actually achieve this.

There are many systems of units in use today, read any news and you will be bombarded with weight in elephants (usually it doesn't specify whether this refers to the African elephant or its slightly smaller relative the Indian elephant), length in busses and volume in Sydney Harbours. The issue facing any unit is how big is it. It has to be well defined so that I can come along with my elephant and confidently say that it weighs 1.143 elephants. This really doesn't make sense so we have a collection of units, the Systeme International (it's French) which at he Metre convention became official global system of units.

So what are the SI units. Starting with the seven base units of Kilogram, Meter, Second, Candela, Kelvin, Mole and Ampere. From these units all other SI units can be derived from these. Those of you in the US and UK are now thinking yeah that's fine but what's wrong with miles and feet and pounds.

Firstly science is done in SI units because they are so much easier to work with. Let's say I run 10 000 m I know this is 10 km because the SI is a prefixed based system. I can also say I ran 10 000 000 mm or 0.01 Mm. With yards and miles you actually have to think. This is really useful for small measurements, the current generation of transistors are 22 nm, if we used inches we are looking at a millionth of an inch. If you are still not convinced we can compare this to the previous generation of transistors at 25 nm, or a millionth of an inch. Unless you want to write out all 6 figures you can't differentiate between the two.

Furthermore when giving the rise of a race feet is generally used, but miles is used for the distance. These are not comparable, and you have to convert to find the gradient. Using SI however you have kilometers and meters and you just need to move a decimal point 3 places. No calculators and minimal thinking involved.

SI is the system of units that has been globally accepted by Metrologists (people that measure stuff) as the standard global system because it is easy to work with. The imperial system is archaic and defined based on the SI units. So seriously, don't use it!