COSC
Also called Swiss Official Chronometer Testing Institute
COSC, the Swiss Official Chronometer Testing Institute, is the independent body that tests and certifies Swiss watch movements as chronometers under ISO 3159.[1]
Its certificate requires a mechanical movement to average between minus four and plus six seconds a day, tested in five positions and at three temperatures over a set period.[1] The test is performed on the movement, before it's cased.
On a pre-owned watch, COSC certification describes how the movement performed when new. The watch's current timekeeping, measured on a timegrapher, tells you how it performs now.
Related terms
Where this comes up
Pages on this site that use the term.
- TUDOR TUDOR Royal 40mm, integrated bracelet, day and dateWatch reference
- TUDOR Black Bay 41, steel on braceletWatch reference
- TUDOR Black Bay 54, 37mm blue dialWatch reference
- TUDOR Black Bay GMT 41mm, burgundy and blue bezelWatch reference
- TUDOR Black Bay Pro 39mm, fixed 24-hour bezelWatch reference
- TUDOR Black Bay Chrono 41mm, tachymetric bezel, steel braceletWatch reference
Learn the trade, not just the word
Plain-English guides to buying, pricing and selling watches as a business. Free, and written to be used at the counter.