Only the Zenith El Primero has survived in its original form until the present day. El Primero’s continuation owes a lot to the demand created by the Rolex Daytona, which from 1988-2000, used a detuned version of the Zenith El Primero 400. Rolex eventually moved away from using Zenith 400, and developed its own in-house automatic chronograph in 2000. The Daytona have since been equipped with Rolex Cal. 4130--an automatic chronograph with vertical clutch, as pioneered 31 years earlier...by Seiko.