Valjoux supplied movements for early Rolex Daytona chronographs. The original Daytona series, introduced in 1963, used a manually wound Valjoux Calibre 72 movement, which Rolex modified and renamed Calibre 722.
Rolex continued refining the design in later references. Calibre 727, based on the same Valjoux architecture, powered models such as the Oyster Daytona references 6263 and 6265. These early watches are distinct from the later automatic Daytonas and are especially prized by collectors.
A common mix-up is Zenith, which supplied the El Primero base movement for the second-generation Daytona reference 16520 beginning in 1988. Rolex heavily modified that movement and called the result Calibre 4030. Sellita and ETA are also associated with Swiss watch movements, but neither is the canonical supplier for the early Daytona chronographs.
The Daytona’s first series was manually wound and used four-digit references, while the 1988 generation introduced automatic winding and five-digit references. That movement history is one of the quickest ways to separate vintage Daytonas from their successors.