Fast becoming a signature complication of the Schaffhausen manufacture, the Calibre 89801 chronograph perpetual calendar with digital date and month display was first bequeathed to the IWC Da Vinci and then the Ingenieur. This year the movement found its way into the Aquatimer, resulting in the collection’s first grande complication model since its inception in 1967. What’s especially remarkable about Calibre 89801 is the perfectly instantaneous date changes for all five discs (two for the date, two for the month, and one for the leap year) every day of the year. This is made possible only with the IWC-developed quick-action switch, a self-contained mechanical energy storage device that builds up power continuously throughout the month, every month. Basically, a special cam raises a spring-loaded lever on this quick-action switch a little bit each day until the end of the month when it falls instantaneously to its starting position.

Limited to just 50 pieces, the Aquatimer Perpetual Calendar Digital Date-Month not only offers traditional complications, it also comes with two other technical features never before seen on any Aquatimer: a patented bracelet quick-change system and an innovative external/internal rotating bezel (complete with IWC SafeDive system). Thus, where previous generations typically come with two crowns – one at two o’clock for the time setting and another at four o’clock for bezel rotating – this new family needs only one.

This new mechanism allows the wearer to time his dives by turning the fluted external bezel and reading the markings off the internal bezel connected via a sliding clutch device. Having an internal bezel protects the mechanism from fine sand particles and seawater, both of which might jam it up if the right conditions are met. For added safety, the bezel turns only anticlockwise.

Switching between a corrugated rubber strap and a stainless steel bracelet is also very simply accomplished thanks to the patented bracelet quick-change system. The bracelet is attached to a locking bar and engages or disengages audibly. Releasing it involves nothing more than a flick of the thumb in the right direction. Cased in red gold with rubber-coated bezel, crown and push-buttons, this 49mm haute horlogerie timepiece ($77,400) may not ever reach 100m or enter the lap pool for that matter, but it would definitely serve you well on any resort vacation.