Standard meter

The meter was initially set as 1/10,000,000 the distance from the equator to the North Pole, but could not be established with high accuracy so was set to the distance between scratches on a rust-resistant metal bar. Now it was set to 1,650,763.73 wavelengths of one of the spectral lines of an isotope of the rare gas krypton.
 France 1960 Standard meter

The meter was initially set as 1/10,000,000 the distance from the equator to the North Pole, but could not be established with high accuracy so was set to the distance between scratches on a rust-resistant metal bar. Now it was set to 1,650,763.73 wavelengths of one of the spectral lines of an isotope of the rare gas krypton.