IWC Schaffhausen Portugieser Eternal Calendar

IWC Schaffhausen recently introduced the Portugieser Eternal Calendar at Watches and Wonders Geneva 2024—a significant advancement in IWC’s perpetual calendar technology, featuring the first secular perpetual calendar which accommodates the complex leap-year rules of the Gregorian calendar. From recognising the varying lengths of months to the additional day in February every four years, it also incorporates a special 400-year gear. This mechanism automatically omits three leap years every four centuries, which will first prove necessary in the year 2100. The watch also includes a highly accurate moon phase display that deviates by only one day after 45 million years, thanks to a newly developed reduction gear.

The Portugieser Eternal Calendar showcases exquisite craftsmanship with a platinum case and a black alligator leather strap from Santoni. It features a glass dial and double box-glass sapphire crystals that enhance the visibility of the complex mechanism inside, contributing to a design that radiates a sense of lightness and understated elegance.

Translating the Gregorian calendar into a mechanical wristwatch format remains one of watchmaking’s most daunting challenges. The Gregorian calendar divides the year into twelve months of varying lengths and identifies leap years as years divisible by four. However, years divisible by 100 are not leap years unless they are also divisible by 400. Thus, while years 2000 and 2400 are leap years, 2100, 2200, and 2300 are not. Traditional perpetual calendars, which are programmed on a four-year cycle, incorrectly treat these centennial exceptions as leap years and thus require manual correction. The Portugieser Eternal Calendar, however, is designed to automatically manage these exceptions correctly until at least the year 3999, thanks to its innovative 400-year gear that completes only one rotation every four centuries.

This gear contains three indentations that strategically skip the three leap years during that period. Despite this complex functionality, the mechanism consists of only eight parts, which emphasizes IWC Schaffhausen’s prowess in creating efficient and technically elegant designs.

The moon phase complication is another area where the Portugieser Eternal Calendar excels. Normally, a lunar cycle does not align perfectly with the calendar month, lasting approximately 29.5 days. IWC’s engineers have implemented a reduction gear between the base movement and the moon phase disc to align the display as closely as possible with the actual lunar cycle. This system was optimized through extensive simulations involving more than 22 trillion combinations to ensure an unprecedented level of accuracy, where the moon phase display will only require correction after 45 million years.

The moon phase itself is indicated through the Double Moon™ display which depicts the lunar appearance from both the Northern and Southern Hemispheres. This feature involves two superimposed discs—a celestial disc with two small openings moves over a static lower disc adorned with a Guilloché pattern, simulating the waxing and waning moons. The Portugieser Eternal Calendar’s dial is intricately crafted, starting with a frosted an lacquered underside, with separately machined and polished subdials that are subsequently attached. The dial’s depth enhances the visual impact of the printed appliques and numerals, creating a floating effect. This is enclosed by box-glass sapphire crystals that are meticulously machined and polished.

Powering the watch is the IWC-manufactured 52640 calibre, which features a highly efficient Pellaton winding system. This mechanism utilizes both directional movements of the rotor to build up a seven-day power reserve in two barrels. Components subject to high stress are made from durable zirconium oxide ceramic. The movement, finished with circular graining and Geneva stripes, is visible through the sapphire glass case back.