Sometimes I think there was a missed opportunity in defining an easy conversion between inches and cm. It is 2.54 cm to 1". Why couldn’t it simply be 2.5? Then a 2x4 from the building supplier could simply be renamed a 5x10. 5.8x11.6 doesn’t quite roll off the tongue as well.
My understanding is that the metre was inspired by nautical measures? So the distance from pole to equator along sea level is supposedly 10000 km. But that’s pretty approximate, and there is a more rigorous definition that involves the wavelength of a certain type of radiation. But that number is quite arbitrary-sounding. Couldn’t they have chosen it to line up with the imperial system at some level to aid migration? Anyway, that train has left the station and I’ll stop ranting now…