IWC Portugieser Eternal Calendar - 45 million years of moon phase accuracy

Arguably one of the most complex watch complications today, the typical perpetual calendar attempts to account for the changes in the number of days in a year due to the additional day in a leap year. However, it doesn’t account for the further complications introduced by the centurial years that are divisible by four. Rather than geek out on this, we’ll refer you to the IWC literature on the subject for the reading pleasure of anyone interested in the relevant details of the Gregorian calendar.

During the Watches and Wonders Geneva event earlier in the month, IWC introduced the Portugieser Eternal Calendar. The watch is a secular perpetual calendar, which unlike a regular perpetual calendar, will not need three corrections over 400 years (starting from the year 2100). The Eternal Calendar watch will be able to accurately calculate leap years up until the year 3999.

If you’re asking yourself why you should care, it’s a fair question. However, though none of us will be here to verify the claims in the only way that matters, watches are often passed to descendants, and they’re likely to appreciate the prowess of the masterful watchmakers who made a mechanical watch to achieve this hundreds of years before their time.

For those planning to live until the year 3999, send us the results of your verification tests when you finally arrive in heaven. In all seriousness, though, putting this level of accuracy in a mechanical watch is a borderline miracle. The Eternal Calendar has an additional mechanism (the ‘400 years gear’) that allows it to do what a regular perpetual calendar can’t. But there’s more to the Portugieser Eternal Calendar:

Moon Phase

The accuracy of moon phase watches has improved over time, with the best watchmakers looking to push the envelope of what’s possible. The Da Vinci Perpetual Calendar, introduced in 1985, had a moon phase precision of 122 years, while the Portugieser Perpetual Calendar, introduced in 2003, had a moon phase accuracy of 577.5 years. Well, IWC isn’t impressed with any of those numbers anymore. The Eternal Calendar watch boasts of a gear that that allows precision in following the moon’s orbit with a deviation of only one day in 45 million years!

Beyond the precision engineering, the Double Moon indication, shows the moon as it is seen from the Southern and Northern hemispheres. It has an upper disk made of glass and a titanium lower disk with a Guilloché pattern, giving the watch an alluring refined look.

Case and Dial

Measuring 44.4mm in diameter with a height of 14.9mm, the Eternal Calendar has a brushed platinum case and a glass dial with a frosted and lacquered white underside. The subdials are separately machined and polished before being fixed to the dial, and the numerals and minute scale are printed on a white flange between the dial and the front glass. All that attention to detail presents a simple yet remarkably elegant look for a watch that does so much under the covers.

Busy at work under the dial is the new IWC 52640 caliber, which features an efficient Pellaton system. It can build a power reserve of 168 hours in two barrels, and you can observe the movement through the sapphire glass caseback.

While the Portugieser Eternal Calendar is still a perpetual calendar watch by definition, it clearly pushes the envelope of what’s attainable in a mechanical watch with the improved accuracy of the moon phase while maintaining a clean and sophisticated look to make it hard to resist.