Watchmakers love to boast about the accuracy of their timepieces. After all, what’s the use of a watch if it doesn’t accurately tell the time? Some watches deviate by several seconds each day, which can add up over time. This is why you might have noticed that your watch is suddenly running a few minutes ahead or behind. Luxury watch brands strive to avoid this by producing extremely precise watches with little variation. The most precise watches are called chronometers.
The Ultimate Guide to Luxury Chronometer Watches
What’s the Difference Between a Chronometer and a Chronograph?
Both chronometers and chronographs measure time, but they measure different types of times. Chronograph watches include a stopwatch function. On the other hand, a chronometer watch is an ultraprecise watch that has passed certain tests guaranteeing its accuracy. A watch can be both a chronograph and a chronometer, but despite the closeness in their names, these terms are not related.
What Is the Definition of “Chronometer”?
The Official Swiss Chronometer Testing Institute is an independent organization that tests and verifies chronometer watches. It’s the most frequently used chronometer certification; it tests over 1.8 million watches a year. Some brands, including Rolex, have their own testing systems.
In French, the institute’s name is Contrôle Officiel Suisse des Chronomètres, which is shortened to COSC. If a wristwatch is a COSC-certified chronometer, that means it has been examined for 15 days and meets the definition of chronometers set by the International Organization for Standardization in ISO 3159. COSC measures seven criteria to test the watch’s precision, putting the watch in different temperatures and positions. The criterion most frequently quoted is the average daily rate, which can be -4/+6 seconds per day. So, the watch can only be four seconds faster or six seconds slower than the reference time every 24 hours in order to be considered a COSC-certified chronometer watch.
Some brands take this commitment to precision even further. Rolex, for example, allows a rate deviation of only -2/+2 seconds per day in its Superlative Chronometer watches. First, Rolex sends its movements to COSC for certification, then it puts the certified movements into their cases. After, Rolex tests the cased watch on its own instruments for 24 hours to ensure a rate deviation below -2/+2 seconds.