Patek Philippe Annual Calendar 5250
In the 2000s, Patek Philippe set up an Advanced Research project to address the long-standing issues of isochronism and durability in watches. The main technology applied to this task was a proprietary alloy of silicon known as "Silinvar". The company proceeded steadily, producing first a Silinvar escape wheel, then a hairspring, an anchor, and a balance.
Ref. 5250 was the first Advanced Research watch, introduced in 2005. Cal. 315 S IRM QUA LU SI included a Silinvar escape wheel, making it one of the first watches ever produced with such a component. The display caseback includes a large "cyclops" magnifier to allow the owner to inspect this high-technology component.
Although it used these high-tech components, Ref. 5250 was nevertheless a Patek Philippe. It included their revolutionary annual calendar mechanism with day and month subdials inset at 10:00 and 2:00, a date window below the moon phase indicator at 6:00, and a simple "+/-" power reserve indicator at 12:00. The dial features Arabic numerals at 3, 9, and 12, applied markers at all other hours but 6, and a "railroad" seconds track. The hour and minute hands are leaf shaped and feature lume. It has a traditional Patek Philippe case in white gold, with long integrated lugs.