What is COSC accuracy?

COSC (Contrôle Officiel Suisse des Chronomètres) certifies mechanical movements that run within -4 to +6 seconds per day. A COSC-certified watch can be labelled as a chronometer on the dial. It is one of the most widely recognised independent accuracy certifications in Swiss watchmaking.

What is Rolex Superlative Chronometer accuracy?

Rolex's Superlative Chronometer standard is -2 to +2 seconds per day — double the COSC precision. All modern Rolex movements undergo COSC certification, followed by an additional in-house test inside a cased watch. The green Superlative Chronometer card ships with the watch.

How do I test my own watch's accuracy?

Set your watch to the exact second using a reliable reference (atomic clock, time.gov, or an app). Wait 24 hours without adjusting, then check against the same reference. The difference is your watch's daily rate. For better accuracy, measure over a week and divide — day-to-day variation evens out with a longer test.

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Movement Accuracy Grader

Last updated: April 2026 · 3 min read

Enter how many seconds your watch gains or loses per day. The tool grades it against COSC, Rolex Superlative Chronometer, and METAS Master Chronometer standards.

Tool

Daily Rate Grader

Seconds per day (use negative for losing, positive for gaining)

Measured ideally over 7 days with consistent wearing posture. A single 24-hour check can be misleading due to positional variation.

Accuracy standards at a glance

Standard	Daily rate	Typical examples
METAS Master Chronometer	0 to +5 s/day	Modern Omega Co-Axial
Rolex Superlative	-2 to +2 s/day	Modern Rolex
COSC Chronometer	-4 to +6 s/day	Many Omega, Breitling, Tudor, Mido
Grand Seiko standard	-3 to +5 s/day	9S mechanical GS
Typical healthy automatic	-10 to +15 s/day	ETA 2824, Seiko, Miyota bases

Movement Accuracy Grader

Daily Rate Grader

Accuracy standards at a glance

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