On the facade of the Ministry of Justice in Paris, just below a ground-floor window, is a marble shelf engraved with a horizontal line and the word ‘MÈTRE’. It is hardly noticeable in the grand Place Vendôme: in fact, out of all the tourists in the square, I was the only person to stop and consider it. But this shelf is one of the last remaining ‘mètre étalons’ (standard metre bars) that were placed all over the city more than 200 years ago in an attempt to introduce a new, universal system of measurement. And it is just one of many sites in Paris that point to the long and fascinating history of the metric system.
“Measurement is one of the most banal and ordinary things, but it’s actually the things we take for granted that are the most interesting and have such contentious histories,” said Dr Ken Alder, history professor at Northwestern University and author of The Measure of All Things, a book about the creation of the metre.