IWC Schaffhausen Receives Guinness World Record For The Latest Portugieser Eternal Calendar

by Sameera Gamage

IWC’s Portugieser Eternal Calendar is the most precise lunar phase wristwatch in the world, and has now been awarded a Guinness World Record for this incredible feat!

During Watches and Wonders 2024, IWC released the new Portugieser line, which featured updates to the brand’s existing perpetual calendar models. Alongside these releases was a Portugieser novelty, a “Tribute to Eternity”. This timepiece is truly unique, with the brand building on its comprehensive expertise in mechanical calendar complications to once again push the boundaries of what is possible.

Guinness World Record Certificate for IWC Portugieser Eternal Calendar

And that is exactly what IWC did. The Portugieser Eternal Calendar is the brand’s first-ever secular perpetual calendar, which takes into account the Gregorian calendar’s leap year exception rules by skipping three leap years over 400 years. The moon-phase display at 12 o’clock has been re-engineered to have an accurate display of 45 million years. A wristwatch created to literally withstand the test of time.

IWC Portugieser Eternal Calendar released at Watches & Wonders 2024

“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.”

Stefan Ihnen, Associate Director Technics of IWC Schaffhausen

IWC Portugieser Eternal Calendar – Case back showing IWC-Manufactured 5260 Calibre movement

Since the introduction of the perpetual calendar complication decades ago, IWC Schaffhausen has been working continuously to update its own perpetual calendar complication and, more specifically, the moon phase display within the complication. The moon phase display is seen as one of the more charming complications in the world of horology, as it displays at a quick glance the current phase of the moon on the dial.

RELATED READING: The Art of Complications – The Perpetual Calendar

IWC’s first perpetual calendar, developed by Kurt Klaus, debuted in 1985. Named the Da Vinci Perpetual Calendar (click the related reading link above to see more information on this timepiece!), it had a moon phase display that was accurate to 122 years. The next major update to the moon phase display came in 2003 when IWC introduced the Portugieser Perpetual Calendar (Ref. 5021). This timepiece had a moon phase display that was accurate to 577.5 years.

IWC Portugieser Eternal Calendar – Assembly of the timepiece

Now, with the release of the Portugieser Eternal Calendar, IWC Schaffhausen has once again pushed the boundaries of it’s perpetual calendar complication. The moon phase display now has a theoretical accuracy of 45 million years, which has been officially recognised by the Guinness World Records as the “world’s most precise lunar phase wristwatch”.

How Did IWC Create The Most Precise Lunar Phase Wristwatch?

In a standard moon phase display, there is a “reduction gear train” placed between the base calendar and the moon phase disc. The whole purpose of this reduction gear train is to reduce what we see as calendar months ending in either 30 or 31 days (except February) so that it lines up with the duration of one synodic month, which equates to 29 days, 12 hours, 44 minutes, and 2.88 seconds. How accurate the moon phase display is to the synodic month is down to the number of wheels used, the dimensions and also the number of teeth each wheel has. The engineers at IWC have created a completely new reduction gear train, one that now features three intermediate wheels, two more than the previous Perpetual model, which had a moon phase accuracy of 577.5 years.

IWC Portugieser Eternal Calendar – Moon Phase Reduction Gear

“To develop a solution that is sufficiently robust and will function reliably for extremely long periods of time, they defined key parameters such as the minimum and maximum number of teeth per wheel. A computer simulation program created specifically for this purpose was then tasked with calculating almost 23 trillion different combinations of wheels and teeth. In an iterative process, the engineers gradually worked their way towards the perfect combination of wheels for this specific application. Assuming a constant duration of the synodic month of 29 days, 12 hours, 44 minutes and 2.88 seconds, the display would theoretically only deviate from the orbit of the moon by one day after 45,361,055 years.”

IWC Schaffhausen on the reduction gear train design for the Portugieser Eternal Calendar

RELATED READING: Our Visit To The IWC Manufacture

The engineers, however, did not stop after the extremely precise design of the wheels was done. To achieve an even higher moon phase display accuracy, the engineers minimised the backlash between the wheels to optimise the tooth geometry. Alternative approaches to the manufacturing process were also needed to ensure that the tiny components function reliably over an extremely long period of time. The engineers opted for the “LIGA process” to manufacture the wheels. The LIGA process involves lithography, electroplating and moulding and is often used in the semiconductor industry. This process permits the production of exceptionally homogenous and smooth microstructures with a degree of precision that conventional manufacturing capabilities would not even be remotely capable of.

IWC Portugieser Eternal Calendar – 400-year Gear Wheel

The end result is the newly developed IWC-manufactured 5260 calibre movement, which features this Guinness World Record moon phase display shown through characteristic Double Moon™ indication. This means that on the dial, both the Northern and Southern hemisphere’s moon phases will be shown. The movement also takes into account the Gregorian calendar’s complex leap-year exception rules. Alongside the reduction gear wheel, IWC developed a newly engineered 400-year gear wheel, which ensures that the calendar automatically skips three leap years over four centuries – an event that will occur for the first time in the year 2100. The movement, with its incredible intricacy, also comes with a staggering 7-day power reserve, which is delivered through two barrels.

The engineers at IWC have undoubtedly raised the bar on the perpetual calendar complication. Rightly so as well, as IWC Schaffhausen was also one of the first to create the modern-day perpetual calendar complication, where all the adjustments to the date, day, and month could be made through the crown. This latest version of the Perpetual Calendar has evolved so much since IWC’s first model. It is exciting to see how much further this complication can advance with the latest technology, experience and the brand’s courage to push the limits of this incredibly complicated mechanism.

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