# how is second standardised

1.The time required for one revolution of the earth is measured by means of an accurate device .
2. This time is taken as 24hours .
3. This is then standardised .
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The?second?(abbreviation, s or sec) is theStandard?International ( SI ) unit of time. One?second?is the time that elapses during 9,192,631,770 (9.192631770 x 109?) cycles of the radiation produced by the transition between two levels of the cesium 133 atom.
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