On the 50th anniversary of the ISO 3159 standard, the Contrôle Officiel Suisse des Chronomètres (COSC) has announced a significant evolution in Swiss chronometry.
Starting in late 2026, the organization will introduce a secondary, more stringent level of certification: the COSC Excellence Chronometer.
This new standard is an extension of, rather than a replacement for, the traditional chronometer certification.
It aims to address modern environmental challenges—such as pervasive magnetic fields and increased power reserves—while moving testing from the movement-only phase to the fully assembled watch.
Under the new 2026 framework, COSC will provide a two-tier hierarchy of performance. Both levels remain strictly independent and involve 100% individual testing (no sampling).
| Feature | Certified Chronometer (Standard) | Excellence Chronometer (New) |
|---|---|---|
| Testing Subject | Uncased Movement | Fully Assembled Watch |
| Base Standard | ISO 3159 | ISO 3159 + Additional Criteria |
| Duration | 15 Days | 15 Days (Movement) + 5 Days (Watch) |
| Daily Rate Tolerance | -4 to +6 seconds | -2 to +4 seconds |
| Magnetic Resistance | Not tested | Up to 200 Gauss |
| Power Reserve | Not verified | Verified against stated specs |
| Testing Condition | Static (5 positions) | Semi-dynamic (simulated wear) |
The “Excellence” certification follows a dual-phase methodology.
First, the movement must pass the traditional 15-day ISO 3159 battery of tests in five positions and at three different temperatures to earn the initial “Certified Chronometer” title.
Once the movement is returned to the manufacturer and cased, the complete watch is sent back to COSC for an additional five-day evaluation. This second phase utilizes robotic systems to simulate 24 hours of average wrist wear.
During this period, the watch must maintain a tightened average daily rate of -2/+4 seconds.
Following the precision test, the watch is exposed to a 200 Gauss magnetic field—representative of daily exposure to electronics like smartphones and tablets—and its power reserve is measured to ensure it meets the manufacturer’s published specifications.
The transition to this new standard began in early 2026 with the integration of new measurement technologies at COSC facilities.
Following pilot tests in March, the formal global unveiling is scheduled for the Watches and Wonders 2026 “LAB” exhibition in April.
The industry expects the first batch of watches bearing the new certification to reach retailers in October 2026.
This move provides brands with a standardized, independent alternative to private in-house “superlative” standards, reinforcing the neutral authority of the COSC in the Swiss watchmaking landscape. cosc.swiss
