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In 1950, Louis Essen determined the speed as 299 792.5 ± 3.0 km/s, using cavity resonance. [112] This value was adopted by the 12th General Assembly of the Radio-Scientific Union in 1957. In 1960, the metre was redefined in terms of the wavelength of a particular spectral line of krypton-86 , and, in 1967, the second was redefined in terms of ...