Kapot horloge teruggestuurd wegens geheime richtlijnen

"soms staat ie een halve seconde naar voren en soms een halve seconde naar achteren"

dat lijkt mij inderdaad niet zo'n groot probleem dat u daarom zou kunnen argumenteren dat het horloge niet goed functioneert. als het horloge per dag achter- of voorloopt zou het anders zijn. de eisen die aan een horloge gesteld worden hangen er ook vanaf of het horloge "chronometer" gecertificeerd is. (zie onder)


so what makes a mechanical watch a "chronometer" or "certified chronometer?"
 
fine watchmakers often have their mechanical watch movements individually certified by the contrôle officiel suisse des chronomètres. cosc is the official swiss institute responsible for certification of wristwatch movements. only watch movements certified with a cosc 'bulletin de marche' (certificate of watch performance) are allowed to bear the internationally protected label "official swiss chronometer" or even use the word "chronometer" anywhere on the product, packaging or advertising.
 
the standard used by cosc is to test the accuracy of a mechanical wristwatch movement--before it is assembled into a watch--for consistent accuracy under a range of position and temperatures. cosc actually peforms seven tests as part of the certification. but the most commonly mentioned is the "mean daily rate" test for which a standard men's watch size mechanical movement, the watch must maintain an accuracy within -4 to +6 seconds of variation per day (that's +99.994% accuracy!).
 
the other six less mentioned measurements are: mean variation in rate, greatest variation in rate, horizontal and vertical difference, greatest deviation in rates, rate variation due to temperature and resumption of rate. overall, these tests measure not only the overall daily accuracy but also the consistency under various normal ranges of conditions.
 
it is also important to note that a "cosc certified chronometer" is not the holy grail of watchmaking. with the high quality of modern manufacturing, this test is nowhere near as important as it was several decades ago. most decent modern watches, when adequately adjusted, should be able to match the performance specified by cosc.
 
a chronometer certificate is not a guarantee of future accuracy. watch movements that have been certified can get out of adjustment and perform poorly. movements that were not certified may still exceed the cosc standards--the manufacturer may simply have simply chosen to bypass the expense of the certification process.