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C.O.S.C.
- contrôle officiel suisse des chronometres
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| The C.O.S.C. is a non-profit association. It was
created by five watchmaking cantons (Bern, Geneva, Neuchatel,
Solothurn and Vaud) as well as the Federation of the Swiss Watch
Industry in 1973. It encompasses the laboratories that had been
established independently of each other from the late 19th century
onwards. |
| A chronometer is a timekeeper precise
enough to be used as a portable time standard, usually in order
to determine longitude by means of celestial navigation. In
the world of watches, the term is also attached to those tested
and certified to meet certain precision standards. In Switzerland,
only timepieces certified by the C.O.S.C. can use the word "Chronometer"
on them. |
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| C.O.S.C. measurement methods: |
| Only the movement is tested
and the tests bear absolutely no relation to a simulation of
watch behaviour and performance when worn. |
| The test is divided into 16 days, 24-hour periods.
The watch is tested in 5 positions and at 3 temperatures. |
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Day
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Temperature
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Position
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0
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23°C
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6 o'clock up / 12 o'clock up (pocket-watches)
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1
|
23°C
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6 o'clock up / 12 o'clock up
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2
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23°C
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6 o'clock up / 12 o'clock up
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3
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23°C
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3 o'clock up
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4
|
23°C
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3 o'clock up
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5
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23°C
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9 o'clock up
|
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6
|
23°C
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9 o'clock up
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|
7
|
23°C
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Dial down
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8
|
23°C
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Dial down
|
|
9
|
23°C
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Dial up
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10
|
23°C
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Dial up. Chronographs run 24 hours
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11
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8°C
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Dial up
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12
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23°C
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Dial up
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13
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38°C
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Dial up
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14
|
23°C
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6 o'clock up / 12 o'clock up
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15
|
23°C
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6 o'clock up / 12 o'clock up
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Criteria
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>20mm Diameter
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<=20mm Diameter
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Pocket Watches
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Mean daily rate: during the first 10 days.
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-4+6 secs/day
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-5+8 secs/day
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-2+5 secs/day
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Mean rate variation: average of the 5 absolute
variations in 5 positions during the first 10 days of
test.
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2 secs/day
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3.4 secs/day
|
1.5 secs/day
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Maximum rate variation: in five positions
during the first 10 days of test.
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5 secs/day
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7 secs/day
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2.5 secs/day
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Maximum difference in rate between vertical
and horizontal positions: mean rate of days 1 and 2 minus
mean rate of day 9 and 10.
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-6+8 secs/day
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-8+10 secs/day
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±4 secs/day
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Greatest rate difference: between one of
the first 10 daily rates and the average daily rate for
the test.
|
10 secs/day
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15 secs/day
|
7 secs/day
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Rate variation according to temperature:
the rate at 38°C minus the rate at 8°C divided
by the temperature difference.
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±0.6 secs/day°C
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±0.7 secs/day°C
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±0.35 secs/day°C
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Secondary error: the difference between
the average rate at 38°C and at 8°C (day 11
and 13) and the average rate with the dial up at 23°C
(day 9 and 10).
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not applicable
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not applicable
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±4.5 secs/day
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Rate resumption: the final rate minus the
average rate of the first two days
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±5 secs/day
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±6 secs/day
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±2.5 secs/day
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