IWC Schaffhausen Portugieser Eternal Calendar Now Holds the Guinness World Records™ Title For World’s Most Precise Lunar Phase Wristwatch

For a watch enthusiast, the moon phase complication holds a special charm. It ensures you never miss a full moon, even if clouds hide it. IWC Schaffhausen has been on a relentless mission to refine the precision since introducing its perpetual calendar nearly 40 years ago.

In 1985, IWC’s master watchmaker Kurt Klaus unveiled the Da Vinci Perpetual Calendar Chronograph (Ref. IW3750), boasting a moon phase accurate for 122 years. Then, in 2003, the Portugieser Perpetual Calendar (Ref. 5021) raised the bar with a moon phase precise for a staggering 577.5 years.Now, the brand topped the expectations once again with the Portugieser Eternal Calendar. This watch features a moon phase complication with a theoretical accuracy exceeding 45 million years, officially recognized by Guinness World Records (GWR) as the “world’s most precise lunar phase wristwatch.”

“The Portugieser Eternal Calendar’s moon phase embodies IWC’s unwavering commitment to engineering excellence and innovation,” says Stefan Ihnen, Associate Director Technics of IWC Schaffhausen. “From our apprentices to our seasoned watchmakers and engineers, we constantly push the boundaries of what’s possible in fine watchmaking. This record is a testament to their dedication and our expertise in the craft.”

Displaying the Moon Phase Precisely Is a Challenge

IWC’s moon phase display relies on a clever gear system. Imagine a train of gears acting as a translator between the regular calendar and the moon phase disc. This “reduction gear train” shrinks a regular month (30-31 days) down to the actual cycle of the moon (roughly 29.5 days). The number of gears and their design determine how accurate this translation is. For the Portugieser Eternal Calendar, IWC’s engineers upped the ante with three intermediate gears, compared to two in the previous model. But it wasn’t just adding gears – they had to find the perfect balance.Think of it like building a bridge. The gears need to be strong enough to last for millions of years, yet precise enough for near-perfect translation. To achieve this, IWC created a special computer program that explored a mind-boggling 23 trillion different gear configurations! Through this iterative process, they identified the optimal combination for unmatched accuracy.

Here’s the beauty of it all: assuming the moon’s cycle stays perfectly consistent (which it does with remarkable stability), this ingenious gear system would only drift by one day every 45 million years!

LIGA Process Offered the Required Precision

While the gear train was a key innovation, it wasn’t the only hurdle. To squeeze out even more accuracy, IWC’s engineers tackled the “play” between the gears, a tiny gap that could affect precision. They meticulously analyzed the tooth design, minimizing this gap for smoother operation.

But achieving long-term reliability for these miniature components demanded unconventional solutions. Traditional metalworking wouldn’t deliver the required precision. The answer? A technique called LIGA, often used in the world of microchips. This process combines light, electricity, and molding to create incredibly smooth and uniform microscopic structures. LIGA’s precision surpasses traditional methods by a staggering degree, ensuring the gears function flawlessly for those mind-boggling millions of years.