The Rolex Chronograph Ref. 6238 “Pre-Daytona” Model

Produced in the beginning of the 1960s to 1967, the chronograph ref. 6238 is one of the last models with a smooth bezel and graduated scale printed on the dial. A casual and sporty watch, its design is more modern compared to earlier Rolex Chronograph watches. Considered the predecessor of the Daytona, the Reference 6238 is known among collectors as the Pre Daytona model.
The first series, introduced around the serial number 1000000, was realized with a Silver monochromatic dial (dark or light with radial shading) or black (more rare). The rarest model contains the medical scale.

Characteristics of the Rolex Chronograph Pre-Daytona Ref. 6238:

Case: Oyster with Push-down buttons, Oyster Twinlock 600 series winding crown, smooth metal bezel, domed plexiglas crystal, monochromatic dial and registers. The most characteristic feauture is the graduated scale printed on dial.

Dial: Rolex Chronograph inscription with unspecified waterproof depth.

Movement: valjoux caliber 72 B (until 1965) or caliber 722 (from. approx. 1965 to 1967).

[Source: Rolex Daytona History and Reference Guide : eBay Guides]

From Wikipedia:

Although Rolex continues to manufacture a version of the “Daytona”, the rarest versions of the Rolex Daytona are the first versions, those whose reference number contains four digits, for example the 6238, 6239, 6240, 6241, 6262, 6263 6264 and 6265 References, produced from 1961 to 1987. The 6238, 6239, 6241 and 6262 References were the first versions, and were not “Oyster” versions, they did not have a screw down winding crown or screw down timing buttons. The movement used was a manual wind Valjoux cal. 72, named the Rolex Cal. 722. The 6263, 6264 and 6265 References were produced commencing 1970, were Oyster versions with screw down crown and screw down timing buttons. The movement used remained based on the manual wind Valjoux cal. 72, but with some refinements, and was called the Rolex Cal. 727. These Daytonas are very rare and very collectible. The movement has proven to be exceptionally reliable and accurate. In fact, the Cal. 727 was certified as a chronometer in some cases.