ChronometerMany people use the term chronometer to refer to any watch or clock - basically any time measurement device. This usage is fine for informal discussion but in the field of horology the word chronometer has a very precise meaning.
What Is A Chronometer?A chronometer is essentially an extremely accurate timepiece. It can be either a clock or a watch - early mechanical chronometers were mainly clocks, those produced today are usually watches aimed at enthusiasts.
The requirement for an extremely accurate chronometer arose from the navigational needs of ships at sea and is closely linked with the issue of longitude. Accurate navigation was almost impossible without accurate timekeeping, and the first effective chronometer was John Harrison's H4 pocket watch.
Because of this association with navigation, many people think of mechanical chronometers as shipboard devices and the term "maritime chronometer" is well known. However as technology improved it became possible to design and build wristwatches to the same degree of accuracy.
The COSCTo formally classify as a certified chronometer, a timekeeping device - be it a clock or watch - must conform to certain standards and pass rigorous tests. The internationally accepted body which makes maintains these standards is based in Switzerland. The Swiss Official Chronometer Control body is known in French as the Controle Officiel Suisse des Chronometres and is hence called the COSC.
Watchmakers send their mechanical movements to COSC who conduct a series of rigorous tests. These check the accuracy of the movement over a period of days as well as other important factors such as the variation in timekeeping depending on the orientation in which it is placed.
If the timepiece passes all the tests then it is issued with an official COSC certificate and serial number.
Modern ChronometersToday we can all buy electronic watches and clocks of astounding accuracy, even some controlled by radio signals. So why should anyone today buy a mechanical chronometer?
The reason is that there is still a market for accurate mechanical watches amongst enthusiasts. Many of these are produced and sold sold by luxury watchmakers such as Rolex which in 1910 was the first company ever to receive COSC certification for a wristwatch.
Controle Officiel Suisse des Chronometres