chronometer
US /krəˈnɑː.mə.t̬ɚ/
UK /krəˈnɑː.mə.t̬ɚ/
1.
an instrument for measuring time, especially one designed to keep accurate time in spite of motion or variations in temperature, humidity, and air pressure.
:
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The ship's captain relied on the chronometer for precise navigation.
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A marine chronometer is essential for determining longitude at sea.