The meter was originally (in 1799) measured as one ten-millionith of the distance from the equator to the north pole. There’s an official meter of this length, in the form of a platinum rod, the “Meter of the Archives,” stored at the International Bureau of Weights and Measures in Paris. Later they made a copy of the Meter of the Archives, the “International Prototype Meter” and from this copy, other prototypes were constructed and distributed to standards organizations around the world and became “National Prototypes.” The United States’ prototype was brought back to Paris four times to double-check its accuracy against the original.
Today the meter is measured as “the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second,” rather than by the platinum rod, because the rod was not quite right (the Earth is thicker around the equator than near the poles due to rotation, a fact not figured into that meter’s reckoning), and because any decent lab can figure out their own official meter using lasers and clocks locally, without reference to the rod in Paris.
Nonetheless the official rod is kept on hand, as an historical curiosity, and just in case the power goes out. When civilization collapses the French will have their meter stick with which to bash the Angles.
Later I’ll try to turn that punchline into a limerick.