Rolex 4030

Caliber 4030 is an automatic chronograph movement manufactured by Rolex. It is a heavily modified version of the Zenith El Primero, incorporating approximately 200 changes from the original design. The frequency was reduced from 36,000 to 28,800 vph, and the movement powered the Daytona reference 16520. Production began in 1989 and discontinued in the early 2000s as Rolex transitioned to its in-house chronograph calibers.