Zenith El Primero 400-based chronograph movement heavily modified by Rolex. Used in Daytona 16520 (1988-2000). Rolex made ~200 modifications, keeping only 50% of original parts. Frequency reduced from 36,000 to 28,800 vph for longevity. Features column wheel, horizontal clutch, Glucydur balance with Microstella regulation, and Breguet overcoil. Last non-in-house Rolex caliber.
Movement Type
Automatic
Jewel Count
31 jewels
Power Reserve
50h
Frequency
28,800 vph (8 Hz)
Diameter
30.5mm
Rotor Type
central_rotor
Winding
automatic_bidirectional
Shock Protection
kif
