Chronometer (COSC) Certification
The Contrôle Officiel Suisse des Chronomètres (COSC) is the independent Swiss organisation that certifies movement precision. Founded in 1973 as a federation of cantonal observatories, it tests roughly 2 million movements per year.
Test protocol
Each movement is tested for 15 days in five positions (CH, FH, 6H, 9H, 3H) at three temperatures (8°C, 23°C, 38°C). Seven criteria must be met, the headline being a mean daily rate between -4 and +6 seconds for movements over 20 mm in diameter.
Manufacturers issued the most certificates
Rolex consistently accounts for the largest share of COSC certifications (regularly above one million annually), followed by Omega, Breitling, TAG Heuer and Mido. Brands such as Omega ('Master Chronometer') and Rolex ('Superlative Chronometer') publish in-house standards exceeding COSC by additional tests after casing.
Key facts
- ▸Founded 1973
- ▸Daily rate tolerance: -4/+6 seconds
- ▸Roughly 2 million movements certified annually