The tachymetric bezel exclusively made in steel, has undergone several upgrades referred to as "Marks/ MK1, 2, 3". This Daytona has the MK3 bezel: graduated from 60 to 400 units. Type 3 font slightly evolved in the A and P series where spacing between the letters in the word "UNITS" is wider. The phrase "UNITS PER HOUR" is located at the 1 o’clock position and "240" can be read whereas "225" and "250" are missing.
The dials also changed. Previous versions came with either matte black or metallic silver dials. On the Daytona "Zenith", the dials were now lacquered and glossy. They also featured applied metal hour markers inlaid with luminous material. And the sub-dials had a thin outer track of an opposing color, each ringed with a metallic edge. Protecting this new dial was a sapphire crystal, used for the first time on a Rolex Daytona.
As it is always the case, Rolex has made subtle tweaks to the Daytona "Zenith" over its lifetime. Most of these concerns the finishing or the text on the dial. In total, experts agree there are 8 distinct "Marks (MK)" or versions of the dial. The Ref. 16520 A series has a Luminova dial (luminova was used in the markers and hands), which is consistent with the watch’s late serial production. The dial also features text on 5 lines, with the words "OFFICIALLY CERTIFIED" reappearing after having disappeared on the earlier MK2 dial. This is a MK8 dial with a regular 6; graphics are in baton style. The 5 lines of text are placed higher up on the dial. The dial bears the words "SWISS MADE" at 6 o’clock due to the use of Luminova (the previous "T’s" for tritium have disappeared). The words "DAYTONA" and "SWISS MADE" are narrower and wider spaced. The spacing between "OYSTER" and "PERPETUAL" was also increased.In outstanding mint condition (un-polished, almost no visible signs of use). Complete with original box, papers and elements (booklets, calendar, sealing wax, inner and outer box).
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In 1963 Rolex debuted in the motor racing competition with the Cosmograph Daytona line with the Ref. 6239. The early models and later production in the next 25 years since its launch, were fitted with manual-winding movements from external manufacturers.
The Valjoux calibre 72 chronograph movement customized by Rolex got the name calibre 72B, later calibre 722, before the upgraded calibre 727 took its place around 1970. Towards mid to late 80’s though, there was a clear trend towards self-winding watches. The thing was that creating a self-winding chronograph movement from scratch is no easy feat. Rolex needed a solution and it came in the form of the Zenith "El Primero" calibre 400, considered the best self-winding chronograph movement available on the market, becoming the clear choice for Rolex who only partnered with the best.
However, Rolex didn’t went through a direct transplant of the "El Primero" calibre into the Daytona and called it a day. Instead, extensive modifications were undertaken to align the new movement with Rolex’s requirements. This evolved movement went by the name calibre 4030. It became the forerunner to the first self-winding chronograph movement produced in-house by Rolex: the mighty calibre 4130 that still powers today’s modern ceramic Daytona models.
Alongside the self-winding movement, Rolex featured several aesthetic updates on the Daytona "Zenith". Most significant was the increase in case size. Whilst previous models had the smaller size of 37mm, the new reference 16520 was a more masculine and sturdy in 40mm, bringing the Daytona in-line with the other professional watches in the Rolex line-up such as the Submariner and the GMT-Master.
The bracelets have had their folding buckle and their end links evolve over time as well. Last series of the bracelet (1999/2000) have polished center links and solid end links (SEL) and a "flip-lock" clasp.
The Oyster case is equipped with screwed pushers, completely waterproofed.