What is a chronometer Watch;What Does It Works

A chronometer is a very accurate and well-made watch and is used by captains of boats in helping to
determine the longitude of the place in which they are. A chronometer is set to Greenwich time and during the
whole of a voyage keeps that time. In order to find his longitude the captain ascertains when the sun has
reached its highest point in the place where he is carrying out the observation. The exact moment is noted and
the chronometer is consulted. For example, it might happen that midday on the ship occurs when the chrono­
meter shows 3 o’clock Greenwich time. As  the earths takes four minutes to turn through a degree of longitude,
this difference of three hours will represent a difference of 180 minutes 4 minutes = 45 degrees. In this
case the ship would be in longitude 450 W.

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