While competitive chronometer testing took place at the observatories in Neuchâtel (1866-1975) and Geneva (1873-1967), testing of large numbers of watches intended for public sale was conducted by the independent Bureaux officiels de contrôle de la marche des montres (B.O.s) established between 1877 and 1956. Between 1961 and 1973, “a chronometer was a precision watch, which was regulated in several positions and at different temperatures and which had received a certificate from the (“B.O.)]" Collective certificates, rather than individual certificates, were usually issued. The 1961-73 standard required a mean daily rate in five positions of -1/+10. In 1973, the B.O.’s came under the C.O.S.C. which specified a daily rate of -4/+6 sec.
Founded in its current form in 1973, the COSC is a Swiss non-profit organization that tests Swiss-made chronometers. COSC is an acronym for the organization's French name, Contrôle Officiel Suisse des Chronomètres.
COSC testing generally applies to watches manufactured/assembled in Switzerland Notwithstanding, the normative standards are set by international agreement and are the same whether they are nominally labeled ISO or DIN standards. Some German, Japanese, and even non-certified Swiss movements can surpass the normative requirements. The Japanese have largely abandoned the accolade, replacing it with in-house testing to a slightly stricter standard as with, for example, the Grand Seiko. On the other hand, the Germans have set up their own testing facility in Saxony at the Glashütte Observatory where the DIN 8319 standards, which mirror the ISO standards used by COSC, are employed. At one time the French provided similar large scale testing at the Observatory at Besançon, however, today only a very few watches are currently tested there and carry the accolade "Observatory Chronometer."
Today, Only 3% of Swiss Watch production is COSC certified, Over a million official chronometer certificates are delivered each year, representing only 3% of the Swiss watch production, a proportion that underscores the exceptional nature of a chronometer. To earn chronometer certification, a movement must not only be made from the highest quality components, but also be the object of special care on part of the finest watchmakers and timers during assembly.
Among others, Ball Watch Company, Breitling submit all their movements for COSC certification, Bremont, MontBlanc, Maurice Lacroix, Chanel, Invicta, Baume et Mercier, Chopard, Chronoswiss, Ebel, Enicar, Girard-Perregaux, Mido, Omega, Oris, Patek Philippe & Co., Rolex, TAG Heuer, Stowa, Ulysse Nardin, Vacheron Constantin, Waltham International and Zenith are brands that submit at least some of their movements for COSC certification. Audemars Piguet, Breguet, IWC, Jaeger-LeCoultre, A. Lange & Söhne, Grand Seiko, Franck Muller and Piaget, Bvlgari are among the expensive brands that do not submit their movements to COSC.
As far as know that Rolex submits almost 40%f of the quota of 1 million watches for COSC certification each year.. So Why Do it like Rolex? Partly their watch are mostly COSC certified. Attached the flagship model fo Rolex, it is a Day Date. The Dial is a newly replaced dial with Pink Good numbering. So this is a new blended way of Art Deco Dial Design..
I am offering this at HKD$42,000.00 with orginal Certificate issues by Rolex Japan, Does it sound attractive!? This Rolex Flagship Day Date is running with -2/+5 seconds a day! well within the sepcification of Kent.