What is COSC certification? What Rolexes have it?
Contrôle Officiel Suisse des Chronometers (COSC) is the Swiss center that tests watch movements. The chronometer specifications are -4 to +6 seconds per day under a variety of temperatures and positions (orientations) for large mechanical wristwatches. COSC also has a test for quartz movements, but it is stricter and less common. In 2001 Rolex certified 761,601 movements (gents and ladies), 573 were OysterQuartz. The movements are tested partially assembled (auto mechanisms, date mechanisms and the like are not installed) and before the movement is installed in the case. After final assembly, Rolex retests the watch. For more information (and to find out what the most accurate movement probably is (hint: it’s a Rolex, but not what you’d guess)) read WatchBore’s Inside COSC article. Information on what models are and are not certified is coming soon.
