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Old 16-10-2006, 10:14 PM   #1916
nautilus
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the timezone Rolex faq got answer about COSC mah..

What is COSC certification? What Rolexes have it?
Contrôle Officiel Suisse des Chronometers (COSC) is the Swiss center that tests watch movements. The chronometer specifications are -4 to +6 seconds per day under a variety of temperatures and positions (orientations) for large mechanical wristwatches. COSC also has a test for quartz movements, but it is stricter and less common. In 2001 Rolex certified 761,601 movements (gents and ladies), 573 were OysterQuartz. The movements are tested partially assembled (auto mechanisms, date mechanisms and the like are not installed) and before the movement is installed in the case. After final assembly, Rolex retests the watch. For more information (and to find out what the most accurate movement probably is (hint: it's a Rolex, but not what you'd guess)) read WatchBore's Inside COSC article.
Information on what models are and are not certified is coming soon.

for more read this > http://www.timezone.com/library/wbor...33384647656250
I would take the Timezone article with a pinch of salt. COSC certification is probably the most overhyped certification in the watch industry. Note that COSC tests only the movements prior to final assembly. This means that there are tons of things that could go wrong AFTER the COSC process. Personally, i would say tests such as JLC 1000hr master control is a far more accurate test as the tests are performed after final assembly. Also, other top end brands do not even bother about COSC as their in-house quality control far surpasses those of COSC. Take lange & sohne for example, every movement is put together, regulated, tested, taken apart, only to be put back together and retested all over again.

With regards to the point on rolex's movement being the most accurate movement out there, is very far fetched indeed. Compared to observatory pieces, rolex's movements (and most others for a matter of fact) differs by a long shot. The best and most accurate movements are usually very hard to come by, observatory pieces, and they're usually equiped with a guillame balance instead of the scantily laser poised, 4 screwed balance that rolex uses. Note that i did not say that rolex movements are bad, rather it's by no means the most accurate movement out there.
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Last edited by nautilus; 16-10-2006 at 10:18 PM..
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