A chronometer is an clock or watch that is extremely accurate at measuring time. Watches must go through a series of tests conducted by the Swiss Official Chronometer Control in order to be designated as chronometers. The institute issues a performance certificate to watches that pass the tests.
The Swiss certificate is highly respected in the watch-making industry, and all watches that pass the tests are considered high-quality timepieces. Seven tests are run by the institute, and the timepiece must pass all seven tests to earn the certificate. Some of the tests include measuring variations in standard timekeeping rates as well as horizontal differences in timekeeping and rate variations due to temperature.