The term ‘chronometer’ is derived from the Greek words ’kronos’ (’time’) and ‘metron’ (’measure’). For a watch to be described as a chronometer, it must meet certain precision standards.

In Switzerland, the Contrôle Officiel Suisse des Chronomètres (COSC) conducts tests and issues certificates to watch movements that meet its standards. A watch containing a movement meeting those standards may use the term ‘chronometer’.

Here is the COSC definition of a chronometer:

‘A chronometer is a high-precision watch capable of displaying the seconds and housing a movement that has been tested over several days, in different positions and at different temperatures, by an official neutral body (COSC).’

On granting certification, the COSC issues the chronometer with a certification number.

The COSC tests are applied to watch movements (ie not completed watches) under certain laboratory conditions and for a certain period of time. They are therefore nothing to do with how a watch may then behave or perform when worn. As far as that is concerned, all the test is saying is, ‘having subjected the movement to certain tests over a specified period of time, we are satisfied that the movement passed our tests’.