The IWC Portugieser Eternal Calendar Is The Culmination of The Brand’s Four Decades of Calendar Expertise

The watch, which accounts for the Gregorian calendar’s leap-year exceptions, remains accurate until the year 3999.
by Yanni Tan

Photo: IWC

In the world of horology, the terms “eternal calendar” and “perpetual calendar” could be used interchangeably, but they signify different levels of engineering and precision. A perpetual calendar is a mechanical watch complication that automatically adjusts for the varying lengths of months and leap years, needing correction only once in a century. An eternal calendar takes this precision a step further by incorporating adjustments for centuries, thus eliminating the need for corrections over hundreds of years.


The IWC Portugieser Eternal Calendar is the manufacture’s first-ever secular perpetual calendar (Photo: IWC)

A masterpiece unveiled

One of the few exceptional eternal calendars to launch this year is IWC‘s groundbreaking Portugieser Eternal Calendar. The manufacture’s first-ever secular perpetual calendar, it marks a significant advancement in the company’s nearly four-decade history in this field. It reaches far beyond the traditional perpetual calendar‘s four-year cycle by accounting for the Gregorian calendar’s complex leap-year exceptions. A newly engineered 400-year gear ensures the calendar skips three leap years over four centuries, an event that will first occur in 2100. This innovation ensures the calendar remains accurate until at least the year 3999, pending future decisions on the year 4000’s leap year status.

One of the standout features of this watch is its moon phase display, which deviates by only one day every 45 million years, thanks to a newly developed reduction gear. This unparalleled precision is achieved by simulating over 22 trillion gear combinations, resulting in a reduction gear train with three intermediate wheels. The moon phase is displayed using the brand’s signature Double Moon indication, showcasing the moon as seen from both the Northern and Southern Hemispheres.

The IWC Portugieser Eternal Calendar features an intricately finished platinum case and a black alligator leather strap from Santoni, exemplifying the manufacture’s dedication to craftsmanship and luxury. The use of glass elements, such as a glass dial and double box-glass sapphire crystals, puts pride of place on the ingenious mechanism inside, creating a sense of lightness and elegance.

This timepiece ensures accurate leap-year calculations until the year 3999 (Photo: IWC)

Programming the Gregorian calendar into a mechanical wristwatch is a monumental engineering feat. The calendar divides the year into twelve months of 28, 30, or 31 days, with leap years adding a 29th day to February every four years. However, only centurial years divisible by 400 are leap years, making 2000 and 2400 leap years, while 2100, 2200, and 2300 are common years. Traditional perpetual calendars, designed for a four-year cycle, incorrectly interpret these exceptions, requiring corrections every century.

The timepiece, however, is mechanically programmed to account for these nuances, ensuring accurate leap-year calculations until the year 3999. This innovation represents a significant leap in horological engineering, underscoring IWC’s commitment to pushing the boundaries of timekeeping.


Double box-glass sapphire crystals allow you unimpeded view of its inner workings (Photo: IWC)

Pushing Further

The IWC Portugieser Eternal Calendar is based on the modular and synchronised design of existing perpetual calendars, allowing all displays to be advanced using the crown. However, it features an additional mechanism that informs the calendar about leap years every four years. This 400-years gear completes one revolution every four centuries, containing three indentations that cause the calendar to skip three leap years during this period. This module, consisting of only eight parts, brings to light IWC’s engineering prowess.

Inside the platinum case lies the newly developed IWC-manufactured 52640 calibre. This high-end calibre boasts a highly efficient Pellaton winding system, building a power reserve of seven days (168 hours) in two barrels. Parts of the winding system, subject to high stress, are made from virtually wear-free zirconium oxide ceramic. The movement, elaborately finished with circular graining and Geneva stripes, can be admired through the box-shaped sapphire glass case back.

This story originally published on The Peak Singapore.

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