DAY- DATE First launched 1956, the Ref. 6511, "Day Date", was for many years one of the most ingenious watches produced by Rolex. Due to the complexity of the watch, with automatic movement, day and date discs as well as a screw-down back, it was a very large and thick watch which gave it an unmistakable presence on the wrist. Introduced as an exclusive model it soon gained in popularity among the world?s elite and as such the ?Day Date? was to become Rolex's flagship model and a status symbol for clients. The first model, Ref.6511, was produced for just over a year before being replaced by the esthetically identical Ref. 6611. This model was fitted with the new calibre 1055 movement with free-sprung balance with its Microstella screws, and was the first Day-Date to have "Superlative Chronometer Officially Certified" on the dial. The Day Date also earned its nickname "President" around this time, when Rolex reportedly gave one to the then President of the United States Dwight Eisenhower. It is believed that President Eisenhower was given this watch at the time of the launch of the concealed clasp on the president bracelet. Rolex designers have, over the years, gradually changed the look from the bubble-back of the early models to the slender shape employed today. The Day Date was available in white, yellow, pink gold, and platinum, with 6 examples being known in stainless steel. With the exception of slight case design changes, the first major modification to the Day Date movement was the addition of the hack feature in 1972, which allowed the wearer to precisely synchronize the watch to a time signal by stopping the second hand when the crown was in the time set position. The next innovation, the "Quick set" feature, solved one of the watches biggest problems: instead of turning the crown through the hours and days to change the date, the button could be pulled out halfway to correct the date. This feature was introduced in 1978 to the Day-Date range and to all Rolex models by 1983. The introduction of the quick set feature coincided with case developments to the Day-Date. The sapphire crystal gave the watch a much thinner look and added to its durability. The early Day-Date models were waterproof to 165 feet (50 meters) while the more robust sapphire crystal allowed them to be rated to depths of up to 100 meters. Around 1984 Rolex introduced a new numbering system that is still in use today, adding an extra digit to the model number. The additional number represented the material. Previously the last number in the 1800 series represented the type of bezel finish; Ref. 1803, for example, has a faceted bezel. The new numbering system on the Ref.18000 series allows collectors to conclusively identify both the case material and finish of the watch bezel. Introduced at the end of 1990, the "Double Quick Set" was the next major change to the mechanism and made it even easier to set, as both day and date functions were set via their own position on the crown. Rolex has also expanded their Day-Date "Crown Collection" by including the setting of various types and cuts of precious stones to the case, bezel and dial, although they have always been available with diamonds on the dial and bezel.