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Below is a collection of posts from different collectors, which outline the very strong similarities and differences between the swiss COSC Chronometer Standard and the Grand Seiko Chronometer Standard. both standards are very similar, with the Grand Seiko requiring one additional positional variance test and slightly tighter tolerances. COSC certified chronometers are tested and certified by the Contrôle Officiel Suisse des Chronomètres, the Official Swiss Chronometer Testing Institute. Grand Seiko certified chronometers are assembled, tested, finished, certified and put into final watches, in house, at Seiko's Morioka facility, the Shizukuishi Watch Studio.

You Can read more about the COSC here:

http://www.cosc.ch/portrait.php?lang=en

You can read more about Seiko's Shizukuishi Watch Studio here:

www.seikousa.com/press/2009/pdf/seikowatchstudios_rls0903-06.pdf


Information about the testing methodologies has been collected from the following sources as well as the quoted posts below:

http://en.wikipedia.org/wiki/COSC

http://www.seiko-watch.co.jp/resourc...al/9S56_02.pdf



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COSC CHRONOMETER STANDARD TESTING METHODOLOGY:

Sources:

http://www.timezone.com/library/wbore/wbore631733384647656250
http://www.network54.com/Forum/78440...+certification


Originally Posted by Glen

1. Over the first 10 Days the average daily rate must be within -4/+6 seconds
2. Mean variation in rate cannot be higher than 2 seconds in any single position
3. Greatest variation in rate between any 2 days cannot be more than 5 seconds in any single position
4. The difference of the rates in the vertical and horizontal positions cannot be more than -6/+8 seconds
5. The difference between the main daily rate and any individual rate cannot be more than 10 seconds
6. Variation in temperature cannot be more than 0.6seconds per degree
7. Difference between the mean daily rate of the first two dates compared with the the last two dates cannot be more than 5 seconds.

There are three labs all located in Switzerland that do the COSC certification: One in Geneve, one in Le Locle, and one in Biel/Bienne. The entire testing process takes 15 days, and the watches are tested in five positions. The watches are tested as movement only, and do not come with hands or anything. Automatic movements have the rotors detached during testing and three temperatures are tested as well. 23 Degrees Celcius is the main temperature tested.

15 Days for Mechanical watches

Day 1 : 23 Degrees Celcius - Vertical - 6 o’clock up
Day 2 : 23 Degrees Celcius - Vertical - 6 o’clock up

Day 3 : 23 Degrees Celcius - Vertical - 3 o’clock up
Day 4 : 23 Degrees Celcius - Vertical - 3 o’clock up

Day 5 : 23 Degrees Celcius - Vertical - 9 o’clock up
Day 6 : 23 Degrees Celcius - Vertical - 9 o’clock up

Day 7 : 23 Degrees Celcius - Horizontal - Dial Down
Day 8 : 23 Degrees Celcius - Horizontal - Dial Down

Day 9 : 23 Degrees Celcius - Horizontal - Dial Up
Day 10 : 23 Degrees Celcius - Horizontal - Dial Up

Day 11 : 8 Degrees Celcius - Horizontal - Dial Up
Day 12 : 23 Degrees Celcius - Horizontal - Dial Up
Day 13 : 38 Degrees Celcius - Horizontal - Dial Up

Day 14 : 23 Degrees Celcius - Vertical - 6 o’clock up
Day 15 : 23 Degrees Celcius - Vertical - 6 o’clock up


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GRAND SEIKO CHRONOMETER STANDARD TESTING METHODOLOGY:

Sources:

http://www32.ocn.ne.jp/~kseiya/gs/
http://www.network54.com/Forum/78440...+certification


Originally Posted by NelsonE

Its tested at 6 positions at a temp of 23 degrees C. Then Dial up at 8 degrees C and 38 degrees C and then a second test at 6 oclock up at 23 degrees C two times. They then give a variation in the first 6 positions at 23 degrees C and daily rates for all positions and tests. In my case my watch ranged from daily rate variations of 0-+4 seconds a day and daily rates of from -9 to +4 seconds a day.from my experience the watch goes from -1 sec a day to +2 sec a day depending on the position its left in at night.

SEIKO ACCURACY STANDARDS:

Sources:

http://www.larrybiggs.net/scwf/index.php?mod=103&action=1&id=1048860541


Originally Posted by Don

Anyone can translate French?

Looking at the numbers, the old test (46 days) is probably spec-ed for a mechanical clock movement.

This is the newer Besancon Marine Chronometer Test Standard for thermocompensated quartz. It takes 47 days.




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In closing, the following is a summary chart comparing the testing methodology of COSC chronometer Standards against those for Grand Seiko's chronometer standards:

 

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