Meter
The distance light travels in 1/x of a second, where x is 299,792,458—the length is measured in terms of the speed of light (x m/s), which never changes.
Example:
Since one meter was defined to be 1/10,000,000 (or one over 10 million) the distance from the North Pole to the Equator in 1793, the meter had since undergone a few definitional changes before its present official definition was agreed in 1983.
Since one meter was defined to be 1/10,000,000 (or one over 10 million) the distance from the North Pole to the Equator in 1793, the meter had since undergone a few definitional changes before its present official definition was agreed in 1983.