COSC Watch Standards¹ Elite Timepieces times most watches we sell.  Watches that meet Contrôle Officiel Suisse des Chronomètres standards are the most accurate mechanical watches in the world.  All COSC watches must meet the standards listed below. Criteria Minimum Requirements (seconds/day) Average Daily Rate -4 , +6 Mean Variation Rates 2 Greatest Variation in Rates 5 Difference in Horizontal/Vertical Positions -6, +8 Largest Variation in Rates 10 Thermal Variation ±0.6 Rate Resumption ±5 ¹ COSC - Contrôle Officiel Suisse des Chronomètres:Mechanical Chronometer ISO 3159, 2012, http://www.cosc.ch/chronometre2.php?lang=en (January 2012).