COSC Introduces Excellence Chronometer, a More Demanding Standard
The Swiss Official Chronometer Testing Institute, COSC, has introduced Excellence Chronometer, an expanded version of its existing certification featuring stricter tolerances and enhanced magnetic resistance requirements. The new standard also includes testing conditions intended to reflect real world use more closely.
Reports of a more stringent COSC protocol first emerged last year. Further details have now been released, clarifying the structure and scope of the updated certification.
Source: monochrome-watches.com
Tighter Daily Rate Tolerances
Under the Excellence Chronometer certification, the permitted daily variation is reduced to six seconds, compared with ten seconds under the traditional COSC standard.
Following casing and the additional evaluation phase, the average daily rate must fall within a range of -2 to +4 seconds per day, instead of the established -4 to +6 seconds required for standard COSC certification.
The decision not to introduce even narrower limits is likely intended to avoid excluding a significant number of market participants, including watches equipped with widely used movements such as those produced by Sellita.
Two Stage Testing Procedure
The first stage consists of the standard COSC examinations, during which uncased movements are assessed against seven criteria defined by ISO 3159.
After successfully completing this phase, the movements are returned to the manufacturer for casing. The fully assembled watches then undergo a further five days of evaluation.
During this second stage, accuracy is checked over a 24 hour period under semi dynamic conditions using a robotic device that simulates wrist wear.
The Excellence Chronometer certification also includes verification of the declared power reserve.
Enhanced Magnetic Resistance
Magnetic resistance forms another key element of the new standard. Watches must demonstrate resistance to magnetic fields of up to 200 Gauss.
By comparison, the baseline industry requirement set out in ISO 764 specifies resistance to a constant magnetic field of 4,800 A per metre, approximately 60 Gauss. A revised version of ISO 764, published in 2020 for watches with enhanced magnetic resistance, requires tolerance of 16,000 A per metre or more, broadly equivalent to 200 Gauss. This value provides the technical basis for the new COSC requirement.
Timeline for Implementation
Pilot trials of the updated procedures are scheduled to take place in COSC laboratories in March 2026 in order to test the processes and support brands during the transition to the new certification.
The first watches certified under the Excellence Chronometer standard are expected to appear in October 2026.
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