Before 1967 the SI units of time and frequency were defined using the tropical year and before 1960 by the length of the mean solar day

Length

In 1983, the meter was, indirectly, defined in terms of the caesium standard with the formal definition "The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second." This implied:
* 1 metre, m, = = c =
* 1 radian,

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