# Wristwatch: What does "chronometer" signify? **URL:** \ **Category:** Factual Questions\ **Created:** [October 17, 2021, 7:48am UTC](https://boards.straightdope.com/t/wristwatch-what-does-chronometer-signify/952632 "2021-10-17T07:48:49Z")\ **Posts on this page:** 1\ **Showing post:** 12
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [October 18, 2021, 12:57am UTC](https://boards.straightdope.com/t/wristwatch-what-does-chronometer-signify/952632/12 "2021-10-18T00:57:44Z")
According to Wikipedia, the certification is based on the ISO 3159 standard: > **[COSC | Standards and methods](https://en.wikipedia.org/wiki/COSC#Standards_and_methods)** > > Each officially COSC certified chronometer is identified by a serial number engraved on its movement and a certification number given by the COSC. > Testing criteria are based on ISO 3159 (Timekeeping instruments — Wrist-chronometers with spring balance oscillator) which defines a wrist chronometer with spring-balance oscillator. Only movements which meet the precision criteria established under ISO 3159 are granted an official chronometer certificate. (Compare ISO 3158.) The certificate is valid ... --- _[View the full topic](https://boards.straightdope.com/t/wristwatch-what-does-chronometer-signify/952632)._