IWC Portugieser Eternal Calendar

Quick specs IWC Portugieser Eternal Calendar
Price: approx. € 153.000 | CHF 150’000 | $ 155,000 | approx. £ 131,000
Size: 44.4 mm
Reference: IW505701

The IWC Portugieser Eternal Calendar is doing things beyond imagination with a 400-year gear and one moon phase deviation in 45-million years. The 400-year gear deals with the leap year exception rules of the Gregorian calendar. And for the moon phase deviation IWC developed a new reduction gear so that a moon phase correction is only needed after 45 million years. Some explanation…

Let’s start with the leap year – and we’ll try to keep it short. A year that can be divisible by four is a leap year, which adds an extra day to February, from 28 to 29 days. However, our years are connected to solar years but these are 365 days, 5 hours, 48 minutes, 45 seconds. Which makes a 1-day correction (during a leap year) not fully accurate.

Compensating the calendar every 400 years

To compensate that, all centurial years that can be exactly divided by 100 are not a leap year unless it can be exactly divided by 400. Then it is a leap year. So, the year 2000 was a leap year and 2400 will be. But a traditionally programmed perpetual calendar will see 2100, 2200 and 2300 as a leap year too, while it’s not. As a result, you need to adjust your regular perpetual calendar three times every 400 years. But not for the IWC Portugieser Eternal Calendar…

IWC’s 400-year gear solves this issue until the year 3999, as it is not yet decided if the year 4000 will be a leap year as well. Well, you’ll not be here anymore anyway. But if your watch survives for centuries, it will still be accurate. The 400-years gear completes just one revolution every four centuries. It has three indentations, and that causes the calendar to skip the three ‘wrong’ leap years in that period.

Moon phase correction in 45 million years

A ‘normal’ moon phase complication needs adjustment every 122 years. One can oversee that. However, in 2003 IWC released their first Portugieser Perpetual Calendar (ref. IW5021) with a moon phase accuracy of 577.5 years. And the astronomical specialists from Christiaan van der Klaauw managed it to push the accuracy to 5,400 years. This with their Christiaan van der Klaauw Real Moon 1980 for instance.

Now, the moon phase display of the IWC Portugieser Eternal Calendar will only deviate from the moon’s orbit by one day after 45 million years. We know that the cycle of the moon does not follow a 30-day rhythm, but a cycle of 29 days, 12 hours, 44 minutes, and 2.88 seconds. To correct this, you need to place a reduction gear between the base movement and the moon phase disc. The more teeth a wheel has, and the more wheels are used, the better the precision becomes.

More wheels for more accuracy

For the IWC Portugieser Eternal Calendar the brand developed a new reduction gear train that uses three intermediate wheels. That mathematically leads to a deviation from the moon’s orbit by one day after 45 million years. It took a computer to simulate more than 22 trillion different combinations in order to find out the perfect quantity of wheels, their proportions and the number of teeth on it.

Developing such a complication is one thing, fitting it in a 44.4-millimeter case with an eternal calendar in it, is another thing. But IWC managed it and is even able to show two moons on the moon phase display. You can see the moon as seen from the Northern and Southern hemispheres.

The IWC Portugieser Eternal Calendar has a power reserve of 168 hours

To show all the complications in a clear way, the platinum timepiece has a white lacquered glass dial with multiple sub dials. And a sub display for a four-digit year indication. Inside the newly developed automatic IWC caliber 52640 runs all the tech. You can admire it through the sapphire case back. It is equipped with a Pellaton winding system with two barrels offering a seven-day power reserve.

The IWC Portugieser Eternal Calendar comes on a black alligator leather strap by Santoni and it is secured with a platinum folding clasp. Given the extreme high-end complications the price is officially on request, but the internet says around 150,000.