The DE razor blade standard reminded me the history of meter, the base unit of length in the SI.
P.S.: National Prototype Meter Bar No. 27, made in 1889 by the International Bureau of Weights and Measures and given to the United States, which served as the standard for defining all units of length in the US from 1893 to 1960. (Source Wikipedia)
- Originally meter was defined as 1/10 000 000 of the distance from the North Pole to the equator.
- Since 1899 meter was defined as the length of a bar made of special alloy of platinum and iridium at the temperature of melting ice.
- Since 1960 meter was defined as a certain number of wavelengths of krypton lamp (0.64 μm, red-orange colour).
- Current definition adopted in 1983 uses the speed of light in vacuum.
P.S.: National Prototype Meter Bar No. 27, made in 1889 by the International Bureau of Weights and Measures and given to the United States, which served as the standard for defining all units of length in the US from 1893 to 1960. (Source Wikipedia)