April 9, 2024: IWC Schaffhausen unveiled the new Portuguese Perpetual Calendar wristwatch at the Watches and Wonders Geneva, a prestigious event in the world of haute horlogerie. Drawing on nearly four decades of expertise in the field of perpetual calendars, IWC broke new ground by introducing its first-ever century perpetual calendar wristwatch. The Portuguese Perpetual Calendar wristwatch not only automatically recognizes the lengths of different months and leap years but also translates the irregular Gregorian calendar into the mechanical program of the watch.
The newly designed gear, calibrated in 400-year increments, ensures that the Portuguese Perpetual Calendar wristwatch automatically skips three non-leap years in every 400-year cycle—a rare occurrence that will first happen in the year 2100. Another notable feature of this watch is its extremely accurate moon phase display. Thanks to a newly developed reduction gear system, the Double Moon phase display™ will deviate from the moon’s orbit by just one day after 4.5 million years. The Portuguese Perpetual Calendar wristwatch features a platinum case paired with a Santoni black alligator leather strap. Several transparent elements, such as the transparent dial, crystal, and caseback with a box-shaped sapphire glass lens, showcase the intricate mechanical mechanisms inside, creating a unique sense of lightness and transparency, embodying understated elegance and aesthetic sophistication.
Converting the irregularities of the calendar into a mechanical program for a wristwatch remains one of the most challenging feats in precision watchmaking. The Gregorian calendar, used in most countries and cultures, divides the year into twelve months, with varying lengths of 28, 30, or 31 days. Leap years occur every four years, adding an extra day to February. However, to keep a perpetual calendar in sync with the actual solar year, an additional adjustment is needed: only the centennial years divisible by 400 are leap years, while other centennial years are common years. This means that years like 2000 and 2400 are leap years, while years like 2100, 2200, and 2300 are not. Traditional perpetual calendars are programmed in four-year cycles, where three common years are followed by a leap year. This would erroneously designate 2100 as a leap year, requiring correction. The same issue arises in 2200 and 2300. In other words, traditional perpetual calendars require three corrections over a 400-year period. The new Portuguese Perpetual Calendar wristwatch (model: IW505701) accounts for these subtle yet complex differences in its mechanical programming. It accurately calculates all leap years up to at least 3999, as the designation of the year 4000 as a leap year has not yet been officially determined.
“Ever since Kurt Klaus pioneered the legendary perpetual calendar in the 1980s, IWC Schaffhausen has accumulated profound expertise in mechanical perpetual calendars, designing highly efficient and user-friendly perpetual calendars. The newly introduced Portuguese Perpetual Calendar watches bring us closer than ever to the limits of perpetuity. We have taken into account the complex leap year exceptions of the Gregorian calendar, automatically skipping three non-leap year century years within 400 years. Upholding the spirit of constant innovation, within this intricately crafted timepiece, we have also equipped it with a moon phase display that remains accurate for 45 million years,” explained Christopher Grainger-Herr, CEO of IWC Schaffhausen.
The watch features a gear designed to skip three non-leap year century years within 400 years.
The design of the Portuguese Perpetual Calendar watch is based on the brand’s existing perpetual calendar module, with all displays adjustable via the crown. Unlike a perpetual calendar programmed in four-year cycles, the Portuguese Perpetual Calendar has an additional mechanism. Every four years, by the end of February, a new module informs the perpetual calendar whether the current year is a leap year. This new module is a gear designed to skip three non-leap year century years within 400 years, and it rotates only once every 400 years. This module, comprising just eight parts, ingeniously addresses the challenge and underscores IWC’s precision craftsmanship.
Moon phase accuracy extends to 45 million years
Since IWC introduced the perpetual calendar forty years ago, the brand has continually improved the accuracy of its moon phase display. The Da Vinci Perpetual Calendar Chronograph (Ref. IW3750) in 1985 had an accuracy of 122 years, while the first Portuguese Perpetual Calendar watch (Ref. IW5021) introduced in 2003 achieved a moon phase accuracy of 577.5 years. Today, IWC’s watchmakers continue to push the boundaries, achieving unprecedented precision in the new moon phase display.
The challenge in displaying the moon phase on the dial lies in the irregular rhythm of the moon’s orbit around the Earth. A lunar month, or lunar cycle, is not 30 days but 29 days, 12 hours, 44 minutes, and 2.88 seconds. Therefore, the length of a calendar month must be reduced to as close as possible to the length of a lunar cycle. To achieve this precision, IWC’s engineers placed a deceleration gear between the base movement and the moon phase disc. The key to achieving high precision in the moon phase display lies in the number, ratio, and teeth of the gears used. IWC employed a special calculation program to simulate over 22 trillion different combinations. They designed a new deceleration gear system for the Portuguese Perpetual Calendar watch, using three intermediate gears. This ensures that the moon phase display deviates from the lunar orbit by only one day after 45 million years. Integrating this new gear system into the narrow space of the perpetual calendar module presented another challenge.
The unique double moon phase display™ on the dial shows the different moon phases seen from the northern and southern hemispheres. This dual moon phase display consists of two overlapping display discs. A celestial disc with two small circular apertures is linked by two points, rotating above a fixed lower disc. This negative phase display gives the appearance of two miniature moons constantly waxing and waning. The lower disc is made of titanium and adorned with a twisted pattern. The upper disc is made of glass.
Exquisitely crafted transparent dials, front and back box-shaped sapphire crystal lenses
The Portuguese Perpetual Calendar watch features a platinum case with a polished and satin-finished surface. Another highlight of the watch is its transparent dial, which is crafted through a highly complex process. First, the bottom of the main dial is coated with white paint after sandblasting. After processing and polishing, the sub-dials are fixed to the main dial. The next steps involve printing and manually installing the dial-mounted hour markers. The depth of the transparent dial gives the printed patterns and applied hour markers a lightness. The unique minute scale and Arabic numeral hour markers on the dial are printed on a white lacquered ring located between the transparent dial and the case. The box-shaped sapphire crystal lens requires complex processing and polishing to form. The Portuguese Perpetual Calendar watch is also equipped with a Santoni black alligator leather strap and a platinum folding clasp.
IWC’s in-house caliber 52640 with seven days power reserve
Inside the platinum case lies the IWC-manufactured caliber 52640. This high-end movement features an efficient Pellaton automatic winding system. The oscillating rotor provides seven days of power reserve to two mainspring barrels, ensuring stable energy supply in both directions. The components of the winding system, which withstand extremely high pressure, are made of virtually wear-free zirconium oxide ceramic. The movement is adorned with circular graining and Geneva stripes, visible through the box-shaped sapphire crystal lens, showcasing the beauty of the movement.
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