In the 2000s, Patek Philippe set up an Advanced Research project which resulted in a series of watches with silicon components. This series culminated in 2011's Ref. 5550 Perpetual Calendar with a full silicon escapement and balance wheel.
Ref. 5650 was a break from this series in many ways. Introduced in 2017, this watch includes no Silinvar components at all and is part of the sporty and less-expensive Aquanaut series rather than a traditional-looking annual or perpetual calendar. For Ref. 5650, the focus is simplification of the complex second time zone crown setting mechanism. Patek Philippe pared down this system from 37 separate components to just 12, using precision stainless steel springs instead of levers and pivots. This improves reliability and also slims the movement height.
The typical Aquanaut case is constructed of white gold and has the prized blue dial. It features a date subdial at 6 00 and a skeleton second timezone hour hand. The hour and minute hands are sword shaped and point to Arabic numerals at 11, 12, 1, 2, 3, and 4. A notable feature is the cut-away dial between 7 00 and 11 00 It is highly unusual for Patek Philippe to have any sort of dial-side “open heart” aperture, but this is in line with the “cyclops” on the back of previous Advanced Research watches in allowing the high-tech components to be viewed.