COSC, or the Contrôle Officiel Suisse des Chronomètres, is the official Swiss chronometer testing institute. It is responsible for certifying the accuracy and precision of mechanical watches. To receive the COSC certification, a watch must undergo rigorous testing over several days in various positions and temperatures. The COSC certification is highly regarded in the watchmaking industry, as it ensures that a timepiece meets strict standards of performance. Watches that pass these tests are awarded a certificate and often display the COSC logo on their dials, signifying their status as a certified chronometer.