Reference 2547 is the most complicated watch ever produced by Heuer. Powered by a Valjoux 723 caliber, the watch not only features day, date and month but also a 12 hour chronograph counter that actually led to its name: "Dato 12". Over the course of its production, this model was manufactured with two case variations, the earlier models with screw back and thicker lugs and the later ones from 1967 to 1971 with a snap on back and thinner lugs.

The present lot, part of the later models, displays a very attractive reverse panda dial with a blue calendar outer scale perfectly matching the blue crescent at the tip of the calendar hand. The small indexes are elegantly placed on the inner section of the dial to ease time reading without overloading the dial's aesthetic. On top of the 12-hour chronograph register, one can identify a T to confirm the use of Tritium on the luminous.

Collectors will be pleased to see that this example is offered on its original Gay Frères bracelet further stamped from the second quarter of 1967. According to the original owner the watch was purchased at the NAAFI in Aden (Yemen) in 1968 for £52. The Navy, Army and Air Force Institutes (NAAFI) is an organization created by the British government in 1921 providing recreational and utilitarian (including supermarkets and shops) establishments on most British military bases.