It turns out that proofreading is a great way to learn new things.

This week, checking a vocabulary-improvement course for teachers of English in Rwanda has unearthed for me some new measurement terms: decimetredecametre and hectometre. We know the more familiar kilometre, centimetre and millimetre, but these other parts of the metric system are rarely used in everyday parlance.

A decimetre (dm) is a tenth of a metre, or 10cm. A decametre (shortened as dam) is 10 metres. A hectometre (hm) is 100 metres. If you know Greek or Latin, you probably worked this out already: deci- comes from the Latin decimus, meaning tenth, but deca- and hecto- are from Greek (deka = ten, hekaton = hundred). Metre itself originates from 1675, when the Italian scientist Tito Livio Burattini introduced the concept of a universal measure, or metro cattolico from the Greek métron katholikón. In French it was mètre, which then came into English in the 18th century.

All very interesting, but what I’m wondering is why we don’t really use dm, dam and hm, apart from in a few specific fields like meteorology and geography. Why does Usain Bolt run the 100m sprint and not the hectometre sprint? Why do we use centimetres all the time, but never decimetres? Come to think of it, why don’t we really use the decilitres (dl: one tenth of a litre) that my Ikea jug is marked with?

I haven’t really got the answers. My research has turned up nothing. I can only assume we say “one hundred metres” because it’s closer than “hectometre” in sound to the old measure of “one hundred yards” – simply put, resistance to metrification. Otherwise, it’s probably just a quirk of our beautifully inconsistent language.