The Rolex Cosmograph Daytona reference 16520, introduced in 1988, is the first automatic Daytona, nicknamed the “Zenith Daytona”. It has a 40 mm stainless steel Oyster case, a tachymeter bezel, a sapphire crystal and screw-down pushers, with water resistance of 100 metres. It runs the calibre 4030, which is Zenith’s El Primero automatic chronograph, modified by Rolex with a lower beat rate of 28,800 vibrations per hour and other changes. The earliest dials carry four lines of text instead of the later two.

Before 1988 the Daytona was a manual-wind watch, and the 16520 gave it a modern automatic movement and a bigger case. Rolex used the Zenith-based movement until 2000, when it was replaced by its own calibre 4130 in the ref. 116520.

The 16520 was ignored at first but is now one of the most sought-after Rolex references, the community prizing the link to Zenith, and prices have risen steeply, especially for “inverted six” and patrizzi-dial examples. It has been out of production since 2000.