COSC Certification
Independent Swiss chronometer certification issued after a movement or watch meets specified precision testing requirements.
Also known as: COSC, COSC certified, COSC chronometer certification, Contrôle Officiel Suisse des Chronomètres
Definition
COSC certification is independent Swiss chronometer testing carried out by the Contrôle Officiel Suisse des Chronomètres. For a conventional mechanical wristwatch movement, the chronometer title is tied to ISO 3159 testing and specified rate criteria; movements are tested under controlled conditions rather than simply judged from a manufacturer's claimed specification. COSC certification concerns the submitted timing device and should be distinguished from schemes such as METAS Master Chronometer, which add testing of the completed watch and additional performance requirements.
Why it matters
COSC gives buyers an independently tested precision benchmark rather than relying solely on a brand's claim. It is useful evidence of tested rate performance, but it does not mean the watch will run at exactly the same rate on every wrist.