Swiss Chronometers and COSC

The C.O.S.C. and chronometer certification: what is it, and what does it mean? 

A chronometer is a watch whose movement has passed specific tests verifying it’s timekeeping precision.  The chronometer testing is open to any manufacturers who wish to submit movements for testing; it is administered in several different locations in Switzerland, two of the busiest offices being located in Geneva and Biel.  The title of chronometer is an earned one and is not something which watch companies can print on the dial of a watch without having undertaken--and passed--the official tests for the specific movement inside that watch.

For many years in Switzerland, annual chronometer competitions were held which allowed watchmakers a chance to showcase the ability of their master “regleurs”, or regulation specialists.  Observatory movements as they were known, were submitted for testing and several different prizes were awarded for the winner and several runners up.  Through these competitions, practical advances in mechanical watchmaking could be brought forth, which resulted in watches which could be ever more accurate and precise.  However, once quartz watches burst on the scene in the 1960's, the quest for ultimate accuracy essentially became a moot point overnight, and the chronometer competitions faded into glorious history.  Yet, as mechanical watches  rebounded in the late 1980's from an obsolete technology to a highly sought after expression of status and ingenuity, the chronometer offices again began to stir.  Now, the Controle Officiel Suisse des Chronometres, (or C.O.S.C. as it is frequently and conveniently referred to), began to find themselves busy providing certificates for the luxury watches which were becoming increasingly popular.

The C.O.S.C. tests only movements, not complete cased-up watches.  The movements are received in batches, which vary in size according to the certification needs of a manufacturer.  At this time, the movements are catalogued, and assigned a unique number by the chronometer office.   The movements are then subsequently monitored by sophisticated equipment which notes the numerical performance of the watch as it undergoes a battery of tests for a period of 15 days.  The tests subject the movements to different temperatures and also orient the movement in different positions, in an attempt to duplicate the great variety of conditions a watch movement will likely be exposed to in use.  Variances in the movement’s ability to maintain an accurate rate are small, and variances between the various positions the movement is tested in cannot be wide.    For the consumer the practical translation of the C.O.S.C. tests translate into a watch that should vary between -4 and +6 seconds per day.  Should this seem lax for those used to the accuracy of an electronically powered quartz watch, keep in mind that there are 86,400 seconds in a day.  A mechanical watch which performs within C.O.S.C. guidelines is right in the vicinity of +99.994% accurate -- most impressive for a complex mechanism of wheels and pinions driven exclusively by the laws of physics!

Quartz movements too, have their own specific tests.  These quartz chronometer tests are different than those for mechanical chronometers, and are considerably more stringent in terms of allowed variation in rate.   Just as quartz watches are more accurate than mechanical ones, quartz chronometers exceed the already high standards of typical quartz watches by a considerable margin.  Few manufacturers bother to certify their quartz movements, but Breitling takes great pride in certifying all of their quartz watch production, which they trademark as "Superquartz".  Rolex's recently discontinued "Oysterquartz" line was another notable quartz chronometer in it's day.  In general, however, most references to the term “Chronometer” refer to mechanical watches, either automatic winding, or hand winding.

While the C.O.S.C. chronometer certificate is an impressive credential for a watch to have, it should also be noted that many watches which do not possess C.O.S.C. bulletins are exceptionally accurate, meeting or even exceeding C.O.S.C. specifications. Indeed, some manufacturers, such as IWC, have in-house requirements which are even more strict than the C.O.S.C. and just choose to forego the expense of certification.  With modern manufacturing methods enabling production of exceptionally precise gear trains and other movement components, it is comparatively much easier to produce an accurate movement today than it was in the past. Further, the chronometer tests only notes the movement performance immediately after testing, and it does not offer a guarantee that the movement will perform the same way as years pass.  Still and all, the chronometer certificate remains a notable benchmark, and provides a useful quantitative means of measuring a commitment to precision.