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Reading through the standards, both are remarkably similar in terms of methodology, with the main difference being the extra position that the GS standard includes. The GS specs are also tighter.

In a nutshell, if the above table makes you go to sleep, a watch that passes the GS standard will also pass COSC's. The converse is not true.

There is also a critical break in the QC process because a certified chronometer movement has to make a round trip to the COSC facility and back before final installation at the manufacturer. All GS movements are assembled, adjusted, certified and installed within the same Seiko facility. This is important because we're talking fine adjustments on bare movements here.

Info compiled from:

http://en.wikipedia.org/wiki/COSC
http://www.seiko-watch.co.jp/resourc...al/9S56_02.pdf


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EDIT - ADDING DESCRIPTORS FOR EACH TYPE OF TEST. (by: Isthmus)

The COSC test methodology, as described here: http://www.timezone.com/library/wbore/wbore631733384647656250 and here: http://www.network54.com/Forum/78440...+certification , is as follows:

Quote:
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[/t][/t]


The GS Chronometer Standard methodology, as described here: http://www32.ocn.ne.jp/~kseiya/gs/ , and here: http://www.network54.com/Forum/78440...+certification

Quote:
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.[/t][/t]
Seiko Accuracy Standards (compiled by Don): http://www.network54.com/Forum/78440...racy+Standards






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.




and here is a comparison of the current COSC standard against the Grand Seiko Standard:

 
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