metre
<unit> (US "meter") The fundamental SI unit of length.
From 1889 to 1960, the metre was defined to be the distance between two
scratches in a platinumiridium bar kept in the vault beside the Standard
Kilogram at the International Bureau of Weights and Measures near Paris.
This replaced an earlier definition as 10^7 times the distance between the
North Pole and the Equator along a meridian through Paris; unfortunately, this
had been based on an inexact value of the circumference of the Earth.
From 1960 to 1984 it was defined to be 1650763.73 wavelengths of the orangered
line of krypton86 propagating in a vacuum.
It is now defined as the length of the path traveled by light in a vacuum in the
time interval of 1/299,792,458 of a second.
(19980207)
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