In 1960 an international agreement defined the metre in terms of the wavelength of the light from which gas, when burnt?
History of the metre to the Doppler effect), and so it was decided to select the orange line of krypton-86 ("λ" ≈ 606 nm) as the new wavelength standard. Accordingly, the 11th CGPM in 1960 agreed a new definition of the metre: The measurement of the wavelength of the krypton line was "not" made directly against the international prototype metre; instead, the ratio of the wavelength of the krypton line to that of the cadmium line was determined in vacuum. This was then compared to the 1906 Fabry–Perot determination of the wavelength of the cadmium line in air (with a correction for the refractive
History of the metre that the original definition had aimed to avoid, so in 1960 a new definition based on a specific number of wavelengths of light from a specific transition in krypton-86 allowed the standard to be universally available by measurement. In 1983 this was updated to the current definition: During the mid nineteenth century the metre gained adoption worldwide, particularly in scientific usage, and was officially established as an international measurement unit by the Metre Convention of 1875. Where older traditional length measures are still used, they are now defined in terms of the metre - for example the yard has since