Pre-owned Rolex Daytona Cosmograph ref 16523 (1996) played an important role in the broader Daytona history as a two-tone “Zenith” model. For those unfamiliar, there are four generally accepted generations of Daytona movements. The first is the manual-wind generation from earlier, vintage models, followed by the second generation of automatic movements, which were furnished by Zenith and the famed El Primero. Rolex modified that movement in-house and dubbed it the caliber 4030. Then, in 2000, the Crown introduced its very first in-house automatic chronograph movement, the caliber 4130. That movement served as the go-to Daytona engine for over two decades before Rolex finally retired it in favor of the current, 4th-generation caliber 4131. For many, these Zenith Daytonas are quite collectible. They represent a time when Rolex was upgrading its staple chronograph to more convenient automatic technology, but right before it had perfected its first in-house movement. Shop Rolex Daytona Collection