WatchesAtlas / Watch knowledgeThe Watch EncyclopediaUnderstand the details that make a watch.Explore watches ↗Find a term or abbreviationCategoryAll categoriesMovements & mechanismsComplications & displaysCases, dials & braceletsFinishing & craftsmanshipPerformance & measurementModern watch technologyCollecting, condition & careSearchAllABCDEFGHIJKLMNOPQRSTUVWXYZ2 termsClear filtersPerformance & measurementChronometerA designation relating to timekeeping performance established through a defined testing or certification process.↗Performance & measurementCOSCThe Swiss organisation certifying chronometer performance through defined tests.↗