IWC Schaffhausen’s Portugieser Eternal Calendar Sets Guinness World Record
The newly introduced Portugieser Eternal Calendar has earned official recognition from Guinness World Records as the “most precise lunar phase wristwatch.” With an extraordinary theoretical deviation of just one day in 45,361,055 years, the Double Moon™ indication of this timepiece surpasses the previous world record by over 43 million years. This remarkable achievement is due to an innovative reduction gear train with three intermediate wheels, which precisely synchronizes one calendar month with the duration of a complete lunar cycle.
Unmatched Moon Phase Accuracy
The moon phase display is considered one of the most enchanting complications in watchmaking, depicting the current phase of the moon on the dial to ensure that no full moon is missed, even if obscured by clouds. Since introducing its perpetual calendar nearly four decades ago, IWC Schaffhausen has continually enhanced the accuracy of its moon phase displays. The first perpetual calendar, developed by former head watchmaker Kurt Klaus, debuted in 1985 with the Da Vinci Perpetual Calendar Chronograph (Ref. IW3750), offering a moon phase accuracy of 122 years. In 2003, IWC advanced this precision to 577.5 years with the Portugieser Perpetual Calendar (Ref. 5021).
The new Portugieser Eternal Calendar takes this legacy further, achieving a theoretical accuracy exceeding 45 million years. This feat has been officially recognized by Guinness World Records, the leading authority on record-breaking achievements since 1955, which meticulously audits each record to meet strict quality standards through a rigorous verification process.
Engineering Excellence
Stefan Ihnen, Associate Director Technics of IWC Schaffhausen, highlighted the innovative spirit driving this achievement: “The moon phase of the Portugieser Eternal Calendar exemplifies the culture of engineering and innovation we live every day at IWC. From our apprentices and trainees to our most experienced watchmakers and engineers, we are continuously pushing the boundaries of what is possible in fine watchmaking. This record is a great recognition of their hard work and our watchmaking expertise.”
The Challenge of Precision
Creating an ultra-precise moon phase display involves placing a reduction gear train between the base calendar module and the moon phase disc. This gear train adjusts the duration of one calendar month to match a synodic month (29 days, 12 hours, 44 minutes, and 2.88 seconds). The display’s accuracy depends on the number and proportions of the wheels and teeth involved. For the Portugieser Eternal Calendar, IWC’s engineers devised a reduction gear with three intermediate wheels—two more than the previous module, which had an accuracy of 577.5 years.
To ensure long-term reliability, key parameters such as the minimum and maximum number of teeth per wheel were defined. A specially designed computer simulation program calculated nearly 23 trillion different combinations of wheels and teeth. Through an iterative process, the engineers identified the optimal combination for this application. Assuming a constant duration of the synodic month, the display would theoretically deviate by only one day after 45,361,055 years.
Precision Manufacturing with LIGA Process
Achieving this level of precision required more than just calculations. Minimizing backlash between the wheels involved optimizing the tooth geometry. Traditional metal machining methods were insufficient, so IWC’s engineers utilized the LIGA process—lithography, electroplating, and molding—commonly used in the semiconductor industry. This process allows for the production of exceptionally homogeneous and smooth microstructures with a precision unattainable through conventional manufacturing techniques.
A New Benchmark in Watchmaking
The Portugieser Eternal Calendar is a testament to IWC Schaffhausen’s dedication to pushing the boundaries of horological precision and innovation. With its recognition by Guinness World Records, this timepiece not only represents a technical marvel but also sets a new benchmark in the world of fine watchmaking.
For more information, please visit IWC.com.
