Watches & Wonders 2024: IWC Portugieser Eternal Calendar Boasts 45-Million-Year Moon-Phase

If you’ve ever wondered what the “Wonders” were at the Watches & Wonders fair (“Isn’t it really all just watches?”), IWC may have come up with an invention that most would agree is truly wondrous (and yes, it is inside of a watch, but still…) — namely, the IWC Portugieser Eternal Calendar, the high-complication flagship of the revamped Portugieser collection that was unveiled at the Watches & Wonders Geneva exhibition this week.

Most watch enthusiasts know IWC Schaffhausen best for its Pilot watches, which are among the most iconic and influential in horological history. What the most studious of these aficionados also recognize, however, is the Swiss brand’s prestigious place in the annals of complicated calendar timepieces, which was secured as early as 1985 with the groundbreaking Da Vinci Perpetual Calendar. At Watches & Wonders 2024, as the high-complication centerpiece of its refreshed Portugieser collection, IWC has achieved the latest milestone in the category, unveiling the aptly named Portugieser Eternal Calendar, the first timepiece whose calendar, leap years and all, will be precise for 400 years without corrections, and whose moon-phase display will remain accurate for an astonishing 45 million years. 

How does the Portugieser Eternal Calendar — which fits all of this near-cosmic level of complexity into a 44.5mm platinum case — accomplish these feats? It starts out with a standard Gregorian perpetual calendar, which accounts for the differing lengths of months and mechanically adds a leap-year day at the end of February every four years. While this is undeniably an impressive mechanical feat, the actual solar year is not evenly divided into 12 months or 24-hour days. Centurial years that are divisible by 400 — like 2000 and 2400 — are leap years while all others, including the upcoming years 2100, 2200, and 2300, are considered “common” years. A perpetual calendar can only be programmed for a four-year cycle (three common years followed by one leap year), and thus the first manual correction to the calendar indications will need to occur in 2100, the first of three corrections over 400 years. IWC’s ingenious invention to deal with this flaw is a newly developed “400 years” gear, which automatically skips three leap years over four centuries, ensuring that the calendar functions are correct until at least the year 3999. This gear, comprising only eight parts, includes three indentations that inform the calendar mechanism which leap years to skip.

If the owner of the Portugieser Eternal Calendar can rest assured that many generations of descendants may never have to worry about setting the date on their inherited timepiece, said owner might also wonder exactly what the planet will look like next time a moon-phase correction is needed. The even more “Eternal” function of the watch is the moon-phase, which is even more precise than the one IWC created for a previous Portugieser perpetual calendar timepiece back in 2003, which offered an unprecedented ongoing accuracy of 577.5 years. The challenge in making a truly accurate moon-phase mechanism lies in the reality that one lunation, from new moon to new moon, does not fit snugly into a 30- or 31-day cycle: it is actually 29 days, 12 hours, 44 minutes, and 2.88 seconds. IWC addresses this with its “reduction gear train” between the base movement and the moon-phase disk; the mechanism uses three intermediate wheels whose proportions and specified number of teeth are able to simulate the more than 22 trillion different lunar scenarios that IWC’s engineers came up with in computer simulations. Mathematically, this means that once properly set, the moon-phase display — in IWC’s hallmark “Double Moon” configuration, which shows the moon as viewed from both Northern and Southern Hemispheres — will deviate from Luna’s actual orbit only by one day after 45 million years.

The movement responsible for all of these wonders is the newly developed Caliber IW52640, which can be glimpsed through an intricately crafted glass dial, with an underside frosted and lacquered in white, with separately machined and polished subdials and hand-applied indexes. A white lacquered flange with the emblematic Portugieser minute scale — yes, this watch still tells the current time in addition to, in IWC’s breathless words, “touching the limits of eternity” — sits between the glass dial and the box-shaped sapphire crystal. The movement features the brand’s proprietary Pellaton winding system and stores a power reserve of 168 hours in two barrels, which means once-a-week winding should be enough to keep the timepiece chugging along reliably for centuries to come.