The launch of the legendary perpetual calendar from Kurt Klaus in 1985 marked the beginning of IWC Schaffhausen’s unique expertise in mechanical calendars. Automatically recognizing the different lengths of the months and adding a leap day every four years, the ingenious mechanism continues to be the benchmark for efficiency and ease of use.

With the Portugieser Eternal Calendar, IWC Schaffhausen once again pushes the boundaries in fine watchmaking. The company’s first secular perpetual calendar is based on the same synchronized design as the regular perpetual calendar, meaning all its displays can be advanced via a single crown. While the perpetual calendar needs an adjustment in centurial years which are not leap years, the secular perpetual calendar is mechanically programmed to consider these exceptions.Thanks to a newly engineered 400-year gear, which completes just one revolution every four centuries, the calendar will skip three leap years over 400 years – an event that will take place in the year 2100 for the first time. The eternal calendar will calculate the leap year correctly until at least 3999, as no official decision has been taken yet as to whether 4000 will be a leap year.

Another highlight of this watch is the eternal moon phase display. IWC’s engineers have taken on the develop a moon phase display with unprecedented precision. After calculating many of more than 22 trillion possible combinations, they devised a reduction gear train comprising three intermediate wheels. The Double Moon™ indication, featuring a titanium base disc with two blue dots and a glass disc rotating above it, will – theoretically – only need an adjustment after 45 million years.

The extensive use of glass elements such as a glass dial and double box-glass sapphire crystals showcases the ingenious mechanism. The glass dial is made in an intricate process.In the first step, the underside of the glass is frosted and then lacquered in white. The subdials are machined and polished separately and then placed on the base plate. Finally, the printing is added, and the appliques are mounted by hand. At work inside the polished, brushed and elaborately finished platinum case is the IWC-manufactured 52640 caliber. The automatic Pellaton winding system uses revolutions of the rotor in both directions to build up a power reserve of 7 days (168 hours) in the two barrels. This extraordinary calendar watch is fitted with a black alligator leather strap from Santoni with a platinum folding clasp.