3 o'clock position), and hours up to 12 hours (at the 6 o'clock position); all of these match the color of the main dial. It also featured a tachymeter scale on the outer chapter ring, and a telemeter chronograph scale on the inner chapter ring. Reference 6234 was succeeded by Reference 6238, which dropped the telemeter scale and updated its appearance to include many features that would be adopted for its successor Reference 6239. Rolex became the official timekeeper of the Daytona International Speedway in 1962, and to mark the occasion, Reference 6234 was replaced with Cosmograph Reference 6239, introduced in 1963 as the first chronograph from Rolex nicknamed "Daytona". However, the original Reference 6239 did not include "Daytona" on the dial (and was in fact nicknamed "Le Mans" for the famous 24 Hours of Le Mans race). In addition to the chronograph features, the wristwatch featured a bezel engraved with a tachymeter, as the watch was intended for racing drivers. Original series The original series, produced in small quantities from circa 1963 to the later 1980s, had a four-digit model or reference number, and had a manual wind movement. The movement is essential to distinguish the original series from the later two series, as the other two movements are self-wound. These first versions with four-digit model numbers are the rarest of the Daytonas. The first version, Reference 6239 featured plain pushers (timing buttons) and did not have the "Oyster" features to enhance water resistance, which include a screw-down winding crown and screw-down timing buttons. Reference 6240 introduced these "Oyster" features to the Cosmograph Daytona in 1965, but the "Oyster" Daytonas were manufactured in parallel with other models which retained the plain pushers until 1972. Various models of the original series could also be distinguished by different bezel materials. The movement used in the original series was a manual wind movement manufactured by Valjoux, which was designated Calibre 72. It was reworked by Rolex and redesignated as Calibre 722. References 6263 and 6265 (produced from 1970) were Oyster versions. The movement used remained based on the manual-wind Valjoux Calibre 72, but with some refinements, and was called the Rolex Calibre 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. Cosmetically, original series Daytonas carried sub-dials in a