Rolex · Automatic

4030

The Zenith El Primero 400 as reworked by Rolex for the first automatic Daytona, reference 16520, from 1988 to 2000. Roughly half the parts were replaced. The beat rate came down from 36,000 to 28,800 to ease wear and lengthen service intervals, and Rolex fitted its own free-sprung Glucydur balance with Microstella nuts, plus a Breguet overcoil in place of the flat hairspring.