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A chronometer is a precision timepiece certified by COSC (or another authority) for exceptional accuracy—achieving ±4-6 seconds per day. A chronograph is a watch with a built-in stopwatch function. These are completely different: a watch can be both a chronograph and a chronometer, or either one independently.
Not always. 'Chronometer' has a specific legal meaning in Switzerland (requiring COSC certification), but elsewhere brands use the term loosely. Always check for official COSC certification or other recognized certifications (METAS, Geneva Seal). Legitimate chronometers display certification details on the dial and include documentation.
COSC-certified chronometers must achieve -4/+6 seconds per day across 15 days of testing in five positions and three temperatures. Some manufacturers (like Rolex with their in-house testing) exceed COSC standards, achieving ±2 seconds per day. METAS-certified Omega watches achieve 0/+5 seconds per day for even tighter tolerances.
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