Units come in all sorts of shapes and sizes. As with most forms of communication the idea is that they give you a common frame of reference when exchanging information. The earliest units tended to be based around bits of anatomy, or obvious, relatively repeatable, physical phenomena. Increasingly complex societies and social interactions required increasingly complex units and increasingly precise measurement of them – that’s how you build pyramids, discover new countries and put the International Space Station in orbit (and keep it there).
The Système international d’unités was developed relatively recently: formal release was 1960, following a period of some 12 years development, although the first unit, the metre, dates back to 1875. You might be more familiar with the SI Units as the metric system, so called after this first unit. The system is formed of seven fundamental units from which pretty much everything else can be defined. So, for example, length is measured in metres, time is measured in seconds, so velocity, the speed at which you are travelling is metres per second, and acceleration, an increase in velocity, is metres per second per second.
Without getting too distracted, these seven units, and the others derived from them, have ‘master’ examples, from which standards are kept around the world. National Measurement Organisations around the world look after these and also seek ever more accurate ways of defining these units, ways which are independent of corruptible, mutable physical constructs – such as the kilogram of platinum.
But what has this got to do with writing a thesis? I’m afraid this is one of those posts which is really for the engineers and scientists rather than the arts, but as this is one of the things that I find I have to correct repeatedly, I think that it is worth setting out exactly what is required when you have to include units in your thesis.
1) You need to have a space between the number and the unit so 1kg is incorrect, write 1 kg instead. A centre dot between the two units is also acceptable – m·s.
2) When one unit is divided by another it is acceptable to present this either as m/s or m s-1 – but, as ever, be consistent.
3) If you have a compound unit, i.e. where two units are combined, then strictly speaking you should have an n-space between the two, i.e. m s or kg mol. The reason for this can be seen most clearly with the former example – if you write ms then people might think that you are talking about milliseconds.
4) If appropriate, you can use your own units: this might be the case if you have a very odd or complex compound unit. However, always double check that there isn’t an existing unit for your situation and that you define your unit carefully and clearly.
In all honesty, this isn’t an exhaustive list, as there will always be local customs, but these four points, if followed, will see you through the majority of problems that arise from trying to present units.