What Is a Chronometer? COSC Certification and the New 2026 Standard, Explained
A chronometer is not a chronograph. A working dealer's plain-English guide to chronometer certification: what COSC actually tests, the -4/+6 standard, how Rolex Superlative and Omega Master Chronometer go further, and the stricter Excellence Chronometer tier COSC introduced in February 2026.