[Tools]

COSC is a certification process to be called a chronometer per Swiss law; it is independent and not affiliated with Rolex.

COSC was instituted in about 1974 and the criteria for testing and passing this chronometer certification has remained the same.

Being certified a Chronometer has little to do with the accuracy of your watch, only that it passed a test where it performed within the criteria. Once tested and passed, a watch is never tested again.