How did the metric meter get its length?

Answer 1

To obtain a standard of length a quadrant of the earth (one-fourth of a circumference) was surveyed from Dunquerque in France to Barcelona in Spain along the meridian that passes through Paris. The distance from the North Pole to the equator was divided into ten million parts to constitute the meter (spelled metre in the International System). The definition of the meter has become more and more precise through the years since, even though its length has not changed. Currently the meter is the distance light travels in a vacuum in 1/299 792 458 second. Other (sub)multiples units of measurement in the metric system are obtained by multiplying and dividing by powers of 10.

Answer 2

One metre is the distance light will travel, in a vacuum, in 1/299 792 485 of a second.

The speed of light in a vacuum is constant, using an older definition of the metre the speed of light was measured at 299 792 485 metres per second. When a more stable standard metre was needed it was defined in terms of the speed of light. Anyone who can measure the speed of light can replicate the standard metre.

Answer 3

In most countries that accomplished it was accomplished by

• setting a date from when all goods would have to be labelled and sold in metric units.
• agreeing a period during which both systems would be allowed to run in parallel.
• setting a date from when things could no longer be sold in non-metric measures.

In some countries (UK, for example), the transition has dragged on and on! Most manufacturers as well as supermarket are required to use metric measures but small traders can still use traditional measures. Beer and cider are still sold in Imperial measures. Road distances and speed limits as well as fuel consumption data are still Imperial.

Schools teach metric units with approximate conversions to Imperial measures but, as soon as the students leave education, unfortunately they need to re-learn the old system.

It used to be suggested, jokingly, that older people would not be able to cope with learning a new system (patent nonsense since countries with far lower rates of numeracy have managed) and so the only solution would have been to wait till all the old people died. The UK has dithered for so long that that suggestion would have worked!