Watch Education — How Do You Tell If A Watch Is A Chronometer?

In order to be classified as a chronometer, a watch has to pass a rigorous array of precision testing.  Over a 15-day period, the Official Swiss Chronometer Testing Institute (COSC) tests the movement of the watch to make sure it adheres to strict accuracy standards.  A chronometer watch must keep time, on average, within -4/+6 or 10 seconds a day.