The purpose of a chronometer is to measure accurately the time of a known fixed location, for example Greenwich Mean Time (GMT). ... Knowing GMT at local noon allows a navigator to use the time difference between the ship's position and the Greenwich Meridian to determine the ship's longitude.

What was a chronometer used for?

Chronometer, portable timekeeping device of great accuracy, particularly one used for determining longitude at sea. Although there were a couple of earlier isolated uses, the word was originally employed in 1779 by the English clock maker John Arnold to describe his sensationally accurate pocket chronometer “no.

What is special about chronometer?

It can measure your heart rate, calculate your average speed, or keep track of two events at the same time. There are also chronographs that have telemetre functions.