> Doesn't sound like a good idea Which is why the CGPM changed the definition of the metre to: - the length of the International Metre (a 9:1 platinum-iridium

> Doesn't sound like a good idea Which is why the CGPM changed the definition of the metre to: - the length of the International Metre (a 9:1 platinum-iridium bar) in 1889; - and then to 1650763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum in 1960; - and finally to the modern definition, the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second in 1983. This means the realisation of the metre depends on the definition of the second.