IWC Portugieser Eternal Calendar

From Here to Eternity: IWC’s Portugieser Eternal Calendar Goes Long at Watches and Wonders

Between its new calendar function not needing adjustment until 3999 and its new moonphase complication being accurate for the next 45 million years, IWC’s Portugieser Eternal Calendar is really living up to its name.

By Laurie Kahle

Ever since the ancient Egyptians devised the sundial around 1500 BCE, makers of various timepieces have endeavored to track the passing of time with ever-increasing precision and reliability. This instinct is as eternal as the astronomical cycles that define our calendar, dividing years into months, months into days, days into hours, and so on.

Given its idiosyncrasies, our Gregorian calendar has long vexed watchmakers seeking to develop the most accurate and longest-running calendar timepieces. Not only do months vary in length, but leap years throw a wrench into the works every four years.

The perpetual calendar presented the solution that accounts for months of different lengths and leap years, but it has its limits.

However, with the launch of the Portugieser Eternal Calendar (Ref. IW505701) at Watches and Wonders Geneva 2024, IWC Schaffhausen introduces its first secular perpetual calendar. This rare and highly technical complication takes the perpetual calendar to the next level by accounting for the complex leap-year-exception rule

What is the Leap-year Exception?

The leap-year exception requires perpetual calendars to pause for adjustment on March 1, 2100. Why? Because in order to keep in sync with the actual solar year, the Gregorian calendar dictates that only centurial years divisible by 400 are leap years, while all others are common years.

This rule designates 2100 as a common year rather than a leap year, throwing off the perpetual calendar’s regular four-year cycle. And since 2200 and 2300 are also common years, a perpetual calendar will need three corrections over a period of 400 years.

The New “400-Years Gear”

However, thanks to IWC’s newly engineered “400-years gear,” the 44.4mm platinum Portugieser Eternal Calendar can (theoretically) track accurate calendar information until at least the year 3999 (since we don’t yet know whether the year 4000 will be a leap year or not).

Building on its four decades of perpetual calendar expertise, IWC based the Eternal Calendar on the same modular and synchronized design as the brand’s latest-gen perpetual calendar, which adjusts all the displays via the crown.

But the Eternal Calendar has a little something extra under the hood: an elegantly designed module consisting of only eight components that can automatically correct for those unorthodox centurial years. This module is the “400-years gear.” It works by completing just one revolution every four centuries and using its three indentations to make the calendar skip three leap years over that period.

A 45 Million-Year Moonphase

When you’re going to such extremes, why stop there? IWC’s engineers also took on the challenge of developing an unprecedented super-accurate moonphase display to pair with their over-the-top calendar.

The lunar month, or the period between new moons, is not a full 30 days but 29 days, 12 hours, 44 minutes, and 2.88 seconds. This discrepancy between the lengths of a lunar month and a calendar month poses a problem for calendar watches that include a moonphase function. To mitigate this, the length of one calendar month must match as closely as possible to one lunar cycle.

IWC addressed this challenge by placing a reduction gear between the base movement and the moonphase disc. However, optimal precision depends on the quantity of the wheels, their proportions, and the number of teeth on each. That is why IWC’s engineers employed a special computer program to simulate more than 22 trillion(!) combinations to come up with its new reduction gear train featuring three intermediate wheels.

As a result, mathematically speaking, the display will deviate from the moon’s orbit by only one day after a mindboggling 45 million years.

The moon’s waxing and waning is charted with the brand’s signature Double Moon display, portraying the moon as seen from the Northern and Southern Hemispheres. The display consists of two stacked discs – a glass celestial disc with two circular openings rotating above a fixed lower disc made of guilloché-engraved titanium with two blue circles representing the moon. The top disc turns to reveal or conceal the blue dots in sync with the lunar phases.

A Secret Weapon: Glass

Glass plays prominently in the Eternal Calendar’s design, resulting in an airy aesthetic which creates the illusion that the printing and hand-mounted appliques are floating in space. The underside of the main glass dial is frosted and lacquered white, while the sub-dials are machined and polished separately.

The balanced layout features the moon phase at 12 o’clock, the date and power reserve at 3 o’clock, the month at 6 o’clock, and the small seconds ringed with the day of the week at 9 o’clock. Meanwhile, IWC’s distinctive four-digit year appears in an aperture between 7 and 8 o’clock, and the Portugieser’s characteristic minute scale appears on the white-lacquered flange positioned between the glass dial and a polished box-glass sapphire crystal (the price for this master work, of course, is strictly on request).

Similarly, a box-glass sapphire crystal caseback showcases the new IWC-manufactured 52640 calibre endowed with a highly efficient bi-directional Pellaton winding system generating a power reserve of seven days across two barrels. As one would expect for a watch of such magnitude, the mechanism is finely finished with circular graining and Geneva stripes.

“Since Kurt Klaus developed his legendary perpetual calendar in the 1980s, IWC Schaffhausen has accumulated unique expertise in mechanical calendars that are ingeniously efficient in their design and easy to use,” said Chris Grainger-Herr, CEO of IWC Schaffhausen, in a press release. “With the new Portugieser Eternal Calendar, we now venture further than ever before, touching the limits of eternity.”

For more information on the Portugieser Eternal Calendar (Ref. IW505701), including availability, check out the IWC website.

(Photography by Pierre Vogel)

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