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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
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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
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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
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23°C
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9 o'clock up
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7
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23°C
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Dial down
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8
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23°C
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Dial down
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9
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23°C
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Dial up
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10
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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
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23°C
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6 o'clock up / 12 o'clock up
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15
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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
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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.
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10 secs/day
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15 secs/day
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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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