I have been living--successfully, I might add--with the metric system for several decades, but knew nothing of its origins. Thanks to another excellent BBC program on measurement of everything (distance, weight, heat, speed, mass, etc.), I know a bit more.
Because of chaos caused by every Tom, Dick, and Harry (or whatever the king/prince/head guy was called) having his own system of measurement, European states agreed with the French academy of science in 1791 to overcome the chaos of multitude measurement systems.
length of meter determined in 1799. Instead of some guys foot, arm, or other appendage length, they agreed to use the earth and chose one ten millionth of distance from north pole to equator. No mention in the program of how that discussion and decision came about, but knowing the French I’m sure they overwhelmed all others with a demand for theoretic beauty. The fact that determining that distance did not matter.
Naturally, measures based upon royal body parts are still in use in US and England, because neither would accept anything with a taint of Frenchness. Initially, only 17 countries signed up, but the kilometer has one the race for world domination.
I also learned another interesting fact: there exists a “master” kilogram (agreed in 1889) in a building outside Paris. Surprisingly, neither the Nazis nor the liberating Americans violated or even entered the building. Once again, those geniuses of yore in France chose to use some aspect of nature to govern a universal definition of weight. The kilogram is based upon the weight of a cubic decimeter of water. To date, only three countries in the world have not adopted the kilogram: Liberia, Myanmar, and--you guessed it-- USA, USA, USA. Who would have guessed.
As far as time goes, which has nothing to do with the metric system, the atomic clock is currently accurate to one second every 138 million years. Because this is so loose, scientists are working to increase accuracy.
Are you not thankful that I have save you the time of looking up all those facts on Wikipedia....