The COSC awards the title of "chronometer" to each watch whose accuracy and consistency of rate has been demonstrated over fifteen days of tests at one of the COSC's Bureaux Officiels (BO). Each watch is tested in five positions and at different temperatures. The COSC is a non profit association created by five swiss cantons, Bern, Geneva, Neuchâtel, Soleure, Vaud. Its headquarters are in La Chaux-de-Fonds. The BO are in Biel, Geneva and Le Locle.
A certificate is issued to an individual watch, not to a model or a range.