Everyone’s talking about... The metric system

Ministers are considering reviving imperial units. So what are the current rules?

Brussels insisted on metric for everything except pints for beer and milk, miles for driving and the troy ounce for precious metals. But it depends how things are sold: you can buy a ‘6ft pole’, but not a length of pole sold by the foot.

What are the benefits of metric?

The world needs agreed standards. Malaysian tribes once measured distance by how many ‘rice-cookings’ away places were. For example, they might say a village was three ricecookings away – meaning you could cook three pots of rice in the time it took to walk there. Hardly universal! Every nation but Liberia has adopted some metrication, if not always easily. The US still largely uses imperial measures (confusingly often different from British ones of the same name), despite passing an act to go metric in 1975. Inconsistency can be expensive: in 1999, Nasa lost a £95million Mars orbiter because one of its teams used metric measures, another imperial.

And metric maths is easier…

Certainly no need to know how many cubits in a furlong etc. Instead, a few base units, such as the metre, scale up in decimal multiples of ten with standard prefixes, such as kilo for a thousand, up to yota for a trillion trillion. Some say that imperial units are more innate as they’re based on human dimensions (though few people’s feet are 12in), whereas a metre is defined as how far light travels in 1,299,792,458th of a second.

How did metric start?

After the French Revolution, to standardise a jumble of weights and measures that varied between towns. The metre was first set as one tenmillionth of the distance from the Equator to the North Pole. Napoleon scrapped metric, but it was restored after his departure. MPs voted for Britain to go metric in 1863, but it didn’t happen until 1965.

Why isn’t time decimal?

The revolutionary French did try, splitting the day into ten hours of 100 minutes, each with 100 seconds. That lasted seven months before being abandoned. China also had a decimal time system up to 1645. That must have been hard to fathom (or ‘hard to 1.829 metres’).