Funnily enough the metre is defined by the globe as well: the arc from the equator to North pole is defined as 10,000 km. I think this might be where the alternative angle metrics came from, which went with the metre:
replyfull circle is 400 grad, so a right angle (10,000 km) is 100 grad.
Then minutes and seconds are factors of 100, so a centesimal minute is 1 km and 1 centesimal second is 10 m.
Originally it was defined like that, but it was fairly quickly redefined as the distance between marks on a prototype platinum bar. It's had a couple of other definitions since then, but it's currently defined "by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit ms⁻¹, where the second is defined in terms of the caesium frequency ΔνCs".
replyYes technically speaking there is a different physical reference now but that's where it came from. A bit like how 1 ft is now 304.8mm but that's because it's the size of a human foot (with some historic details no doubt).
replyEtymology vs dictionary, I suppose.
But that isn't a change to the definition of the meter. What do you think the motivation for the constant 299,792,458 is?
reply> that isn't a change to the definition of the meter
replyHow is it not? it's not a change to the actual distance (well, it is for a sufficient precision), but a change to the definition of the metre is exactly what it is. It's defined relative to the speed of light rather than a random platinum bar length, with the constant picked so that the actual measurement stay the same (up to a certain level of precision).