Contrôle Officiel Suisse des Chronomètres translates into English as the Official Swiss Chronometer Testing Institute, but everyone just calls it COSC. Some say ?cosk? and others, like me, just say the individual letters. COSC?s job is to measure and certify the accuracy of mechanical watch movements, specifically to guarantee that a watch will run within +6 to -4 seconds per day.
Watches without COSC-certification can still run within those tolerances, but that?s typically a matter of luck rather than fine-tuning. With COSC-certification, you know that the watchmaker fussed over the movement in order to prepare it for COSC?s scrutiny, and once it is certified the watch can officially carry the heavy-weight title of ?OFFICIAL CHRONOMETER.?
Back when mechanical timekeeping was all we had, COSC-certification was a crucial designation. By the 1970s, quartz movements downgraded the importance of mechanical accuracy, and today COSC-certification is really the plaything of mechanical watch connoisseurs.
Click here for our four-part “History of Chronometers.”

For that reason, more than a few folks scoff at COSC-certification as an unimportant, perhaps antiquated, program that?s mostly there to bump up the price of a watch. However, such scoffing is beginning to sound a bit off-key as prices for COSC-certified mechanical watches have been falling recently. Regardless of where you stand on the topic, it?s getting harder to argue that COSC-certification is out of r...