 In 1907 , the International Astronomical Union defined the international <unk> in terms of a red cadmium spectral line ( 1 wavelength = <unk> @.@ <unk> <unk> ) . This was adopted by the 7th General Conference on <unk> and Measures in 1927 . In 1960 , the definitions of both the metre and <unk> were changed to use krypton . 
