Rolex Cosmograph DaytonaRolex started making chronographs in the 1930s, but it was only in 1963 that a named product line was introduced: the Cosmograph. In some early advertisements, Rolex referred to the watch as the ‘Le Mans’ after the famous race track in France, although the name never appeared on the dial. After a few years, the line was officially renamed Cosmograph Daytona, after the racetrack in Florida.The most noticeable difference between these Cosmograph (Daytona) models and earlier Rolex chronographs was the tachymeter scale (used for measuring distance and speed) that was moved from its traditional placement on the dial to the bezel. Furthermore, the dial was updated with the introduction of contrasting sub-dials.It's hard to imagine now, but Daytonas received little love after their release. Most Daytonas languished in dealer displays for years and only started to get noticed by Italian collectors and dealers in the late 1980s. Nowadays, Daytonas are among the most sought after Rolex models, fetching prices from $20,000 for modern ones to many millions for rare vintage references. A big contrast with the $210 list price when it was first released!Waterproof 62xx DaytonasEver since the invention of the ‘Oyster case’ in the 1930s, Rolex has been marketing the waterproof capabilities of its watches. However, the first truly waterproof Daytona only came into existence in 1965 thanks to the introduction of the ref. 6240 and its screw down chronograph buttons (instead of the round pump pushers with internal gaskets on earlier Daytonas). The 6240 was also the first Daytona to feature a black acrylic bezel inlay with contrasting white graduation scale. The 6240 was discontinued after just 4 years and was replaced by the 6263 in 1969. The 6263 (and its brother, the 6265, with a metal bezel) enjoyed the longest production run of all vintage Daytonas (1971-1987).