An atomic clock - which measures the frequency with which atoms move in and out of excited states.
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The sundial
Timepieces.
In the past, a common time measuring instrument was the sundial. Today, the usual measuring instruments for time are clocks and watches. For highly accurate measurement of time an atomic clock is used. Stop watches are also used to measure time in some sports.
You would possibly use a chronometer which is an extrememely accurate clock.You would possibly use a chronometer, a very accurate clock.
You can measure kilometres in metres, which would be 1000, or decametres, that would be 100, or in hectometres, that's 10. You could even measure in decimetres