Since the Middle Ages, science and commerce had been saddled with a host of customary units such as pieds and pouces, that varied from region to region. What was needed was a universal, logical system, based on pure maths and immutable standards.

A committee set up by the French Academy of Science recommended a decimal system, since this would make calculations immeasurably simpler. And in an attempt to peg that system to some immutable natural phenomenon, it chose the Earth itself as a starting point. Accordingly, a new measure - a metre - was proposed, that would equal one 10-millionth of the distance from the pole to the equator along the meridian passing through Paris. But there was one snag. Nobody had a clue what the circumference of the Earth was.

In 1792, Jean Charles Borda (pictured above) decided to measure the distance from Dunkirk to Barcelona and work it out from there. It took him six years. But in 1799, the metric system was finally made official with the production of three easy-to-check platinum and iron “standards”, and there was no going back.

No sooner had the unit length been fixed, however, than its basis began to look increasingly arbitrary. The discovery within a few years that the Earth, being flattened at the poles, is not perfectly spherical caused much consternation, further undermining the authority of an already unpopular system. Subsequent attempts to link the metre with the dimensions of the Earth have failed, and scientists today define it as the distance travelled by light in a vacuum in 1299,792,458 of a second.

Worth bearing in mind next time you find yourself with a shelf to put up.