Navigation clock was found in late 17th century when the ocean navigation have no other ways to measure longitude but to use precise navigation clock to record then and time difference between the prime meridian and noon time, and then calculate the time difference and difference of longitude. Therefore, the ocean navigation requires a pretty accurate navigation clock. during the 18th century and middle 20th century, main astronomical observations in Europe serves as bodies to test clocks’ precision, including the Kew in Britain, Besancon in France and Geneva Astronomical Observatory. They periodically tested those navigation clocks and score them and ranked them. So all quality test are called Astronomical Observatory Test.
But COSC is a non-profit organization and was found in 1973. It was set up by 5 clock plants and the COSC means controle officiel suisse des chronometers, but actually have little connection with astronomical observatory. The standard for mechanical watches is to satisfy requirements from ISO 3159, which requires the daily difference between minus 4 and plus 6 seconds. Some brands from Japan and Germany may surpass that criterion. This is not a severe standards, and some, like Patek Philippe and Piaget exceed them. The old rules from astronomical observatory required scored and ranked the watch, while COSC just set up a minimum. All that could pass the tests will be a Chronometer. It is said that only Girard-Perregaux watches based on is 32A movements get high scores and now quite a pretty number of watches could not called Chronometer.
So far, COSC also test quartz movements, and it’s more strict on quartz movement, which only +0.07 and -0.07 second difference is allowed. What’s more, COSC only tests movements instead of the whole watch. after passing it, the movement will be sent back to plant to do the final assembling.Tags: brief, introduction