All watches are not created equal.

Some are "certified chronometers," which is not to be confused with mere chronographs. All watch enthusiasts know that COSC stands for Controle Officiel Suisse des Chronometres. A watch movement that is COSC-certified is more desirable than one that does not because it has been "officially" tested for extreme accuracy under controlled conditions.

The COSC is an independent agency in Switzerland that charges watch manufacturers a small fee (5 Swiss Francs or about $3.00 US) to test their movements. It does not test watch models. Just movements.

When a watch manufacturer sends a quantity of watch movements (or calibres) to be tested, the COSC subjects individual movements to a rigorous 15-day ordeal at three different temperatures, testing the watch movements in five different positions.

Men's watch movements (defined as those calibres taken from cases 20mm in diameter or larger) are tested to higher standards than smaller women's watch movements (so much for equality). Watch movement that do not exceed the mean (average) deviation by two seconds gained or lost over a 24-hour period and measured at different temperatures and in various positions are awarded the Chronometer Certificate.

Watches that have passed the COSC testing sometimes include the numbered certifiate or a replica of it with the watch papers, and many brands (such as Rolex) make certification statements on the watch face ("Superlative Chronometer Officially Certified").

Other watchmakers (Audemars Piguet, Patek Philippe, and others) all but ignore the COSC, which is not to say they do not produce excellent timepieces.

If you are wondering how the COSC can manage on $3 per tested movement, consider that in 1999 they tested 982,000  movements! Their largest customer is Rolex, which in that year sent 585,000 calibres for testing. Omega followed with 138,000 and Breitling tested 128,000. Far behind in testing numbers were Bulgari (22,000) and TAG Heuer (13,000), with Panerai close behind at 12,800. On the next tier with 1,200 to 5,000 movements tested were Vacheron Constantin, Tissot, Concord, Zenith, Ebel, Swatch, Glashutte, Ulysse Nardin (and a few others).