Million Year Moon: The IWC Portugieser Eternal Calendar

Trade shows serve many purposes but one of the most enjoyable for all and sundry is the introduction of so-called talking pieces – often, but not always, complicated watches (although depending on what brand you are, you can get people talking with something as minor as a new dial design on an existing model). One of the most interesting talking pieces at Watches & Wonders this year is a new perpetual calendar from IWC – the aptly named Portugieser Eternal Calendar.

IWC is famous for its perpetual calendars, largely thanks to the work of watchmaking legend Kurt Klaus, who designed the IWC perpetual calendar mechanism first introduced in the Da Vinci Chronograph Perpetual Calendar, in 1985. The Kurt Klaus perpetual calendar mechanism was an early example of a so-called synchronized perpetual calendar, in which all of the calendar indications could be set simultaneously with the crown. Another notable feature of the design was the use of a four digit sliding year indicator – the first of its kind, and the first versions of the mechanism included a century slide, allowing the watch to show the correct year until 2499. The Portugieser Eternal Calendar, however, takes the question of reckoning the passage of centuries one step further – it’s IWC’s first secular perpetual calendar, which is capable of showing the correct length of every month, every year, and every century, until at least the year 3999.

A conventional perpetual calendar shows the correct length of all months with 30 0r 31 days, and it also handles the 28 day length of February. Perpetual calendars can also correct for a Leap Year, adding the 29th of February once every four years. What they can’t do, however, is handle the fact that every 100 years, the 29th of February is omitted, in order to correct for the fact that adding an extra day once every four years is not a completely accurate correction. And, in addition, for every century year divisible by 400, you have to add a leap day back into February again. This means that a conventional perpetual calendar needs to be corrected three times over a 400 year period. The secular perpetual calendar, on the other hand, can handle the full 400 year cycle of Leap Years.

The 400 year module being installed

The reason IWC is hedging its bets a little and saying “at least until the year 3999” is because, while by the rules of the Gregorian calendar, 4000 should be a leap year, it’s also true that even the 400 year rule for the Gregorian calendar still leaves over a small error (according to some sharp folks on the Math Stack Exchange, 1.2 days). That’s what happens when you have a tropical year that fits into a whole number of days, but fortunately we can leave that problem to whomever cares about calendar reform two thousand years from now.

The 400 year module is visible through an opening in the glass dial.

The 45 million year moonphase is a record breaker. Kurt Klaus developed a 122 year moonphase for IWC in 1985, and until the Portugieser Eternal came out their most precise moonphase had an error of one day every 577.5 years. In 1999, A. Lange & Söhne released the 1815 Emil Lange moonphase, which had an error of one day every 1058 years. Ochs und Junior’s moonphase is precise to one day in 3,478.27 years; Christiaan Van Der Klaaw’s spherical moonphase complication is accurate to one day’s error in 11,000 years. And then there is the former record holder, Andreas Strehler’s Sauterelle à lune perpétuelle – accurate to one day’s error in 2.045 million years. IWC says that calculating the correct ratios for the three gear train for the moonphase required a computer simulation that tested 22 trillion combinations, and since we are dealing with absurdly big numbers, if the simulation could test one combination per second, testing 22 trillion combinations would require 697,615 years (I’m rounding off).

The Portugieser Eternal Calendar also has a multi-layered dial constructed from glass – another first for IWC. The base dial is frosted and coated with white lacquer, and then the subdials are placed on top. The moonphase display consists of two immobile dark blue circles, over which a glass disk rotates, which has two cutouts; it’s the glass disk which is driven by the moonphase gear train.

The whole idea of an ultra precise moonphase is a little bit of a pipe dream, of course. For one thing, calculating the gear train for any moonphase complication means you have to pick a number for the length of a lunar month, and the lunar month actually varies in length – the average length of a lunar month is 29.53059 days but that varies in any given year thanks to the precession of the Moon’s orbit. The other thing to bear in mind is that 45 million years is a long time – for one thing, you can bet that humans will either be extinct in 45 million years or will have evolved into something else (I’m Team Prehensile Tail myself) and the Earth is going to look very different, thanks to continental drift (Africa is going to drift far enough north that in in 45 million years the Mediterranean Sea will have closed up). And the Moon, more germanely, is going to be further away. According to NASA the Moon recedes at a rate of about 1.5 inches per year, which in 45 million years adds up to 1065 miles – about half the Moon’s diameter.

Still, there is something intellectually satisfying about a mechanism that encodes a natural cycle with such precision, even if that precision reflects a snapshot of the current situation, rather than how it will evolve. Maybe that’s the real reason, if you can call it that, for making watches with complications so precise that eventually the natural world will depart from that precision – a way of getting us to consider the nature of time itself, and just how deep so-called deep time really is.

The IWC Portugieser Eternal Calendar: Case, 44.4mm x 15mm, in platinum; 5 bar/50M water resistance; glass dial with white lacquer, rhodium plated hands and Arabic numeral appliques. Movement, IWC caliber 56240, Pellaton winding system; secular perpetual calendar, with four digit year display; moonphase for Northern and Southern hemispheres, accurate to one day in 45 million years; stop seconds, 18k gold rotor with see through sapphire caseback. Price, available on request. For more, visit IWC.com.