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IWC Portugieser Eternal Calendar Features Moonphase Accurate for 45 Million Years

IWC Portugieser Eternal Calendar

In watchmaking, calendar complications are everywhere. Technically your time and date watch is a form of calendar, although the least prestigious kind as it needs resetting five times a year whenever a month doesn’t have 31 days. Essentially, the less often a calendar watch needs correcting the more prestigious it is, as it means that it can mechanically account for the nuances and peculiarities of the Gregorian Calendar. At the absolute pinnacle of calendar watchmaking is the secular perpetual calendar, a complication that IWC have attempted for the first time with their new watch, the Portugieser Eternal Calendar.

In order to understand why the secular perpetual calendar is so impressive, you need to understand how the Gregorian calendar works across centuries of time. Unsurprisingly, it all comes down to leap years – the phenomenon whereby every four years an additional day is added to the end of February. However, there’s also a nuance whereby in centenary years there is only a leap year if the year is also divisible by 400. So, the year 2000 was a leap year but the years 2100, 2200 and 2300 won’t be, and then the year 2400 will be. A standard perpetual calendar will assume that all of these years are leap years, which is why you’ll often see brands saying the next time their perpetuals need updating is the year 2100.

IWC Portugieser Eternal Calendar

A secular perpetual calendar can account for these centenary years, skipping three leap years across a 400 year period. That means they will stay accurate to the Gregorian calendar indefinitely. In fact, the only limitation and the reason brands can’t advertise that their watches will be accurate forever, is that humanity itself hasn’t decided if the year 4000 will be a leap year or not. These watches are even rarer than perpetual calendars and we don’t exactly have perpetual calendars coming out of our ears.

The IWC Portugieser Eternal Calendar accomplishes this by adding a new module consisting of 8 parts to its perpetual calendar movement. This module is called the 400-year gear and quite simply it’s a gear that completes a rotation once every 400 years and which has 3 indentations that cause leap years to be skipped. Considering the social media furore that rocks up every four years of collectors sharing their perpetual calendars ‘doing the thing’ on February 29th, imagine the anticipation of the owner of a secular calendar at the dawn of a century. A once in a lifetime horological experience.

IWC Portugieser Eternal Calendar

However, that’s not the only impressive mechanical feat of the Eternal Calendar as it’s also equipped with a new hyper-accurate moonphase mechanism. The engineers at IWC simulated over 22 trillion possible gear train configurations to find the most accurate possible mechanism and the resulting moonphase will only deviate by a single day after 45 million years. To put that into perspective, humanity has existed for around 300,000 years, which equates to approximately 0.7% of 45 million years. This level of accuracy borders on inconceivability.

IWC Portugieser Eternal Calendar

Since we’ve already talked about the movement so much already, let’s continue. It’s called the IWC manufacture calibre 52640 and it’s an automatic movement with a 7-day power reserve. Which is an absolute blessing because all of those amazing technical feats of accuracy are pre-requisite on the watch staying wound constantly. If the watch stops working because of the power reserve then obviously it won’t keep time properly and will need resetting. A reliable watch winder definitely a worthwhile investment here.

Zooming out from the movement at the core of the IWC Portugieser Eternal Calendar, we come to the case and dial. The watch has a 44.4mm diameter x 14.9mm thick case made from platinum with a double-box glass sapphire crystal. Glass is an important material because the white lacquer dial is also made from it, giving certain elements like the Double Moon™ phase a translucent property.

The display itself is fairly conventional for a perpetual calendar. It has central hour and minute hands, with the moonphase at 12 o’clock with a scale and hemisphere indicator. At 3 o’clock is a subdial for power reserve and date, at 6 o’clock is months, between 7 and 8 is the year and lastly at 9 is the small seconds and days of the week.

IWC Portugieser Eternal Calendar

It’s priced at CHF 150,000, making it one of the most expensive watches in IWC’s current range, similar to the Lewis Hamilton Portugieser Tourbillon Rétrograde Chronograph, another platinum timepiece. The Eternal Calendar is a seriously impressive piece of engineering, backed up by a display that’s fairly industrial with its translucent glass, bordering on ascetic. A dedication to watchmaking as a science.

Price and Specs:

Model: IWC Portugieser Eternal Calendar
Ref: IW505701
Case: 44.4mm diameter x 15mm thickness, platinum
Dial: White lacquered glass
Water resistance: 50m (5 bar)
Movement: IWC calibre 52640, automatic, 54 jewels
Frequency: 28,800 vph (4 Hz)
Power reserve: 168h
Functions: Hours, minutes, seconds, eternal calendar
Strap: Black alligator leather
Price: CHF 150,000

More details at IWC.

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About the author

Michael Sonsino

As Digital Editor for Oracle Time, Michael needs an eye for detail, which makes it a good thing that his twin joys in life are miniatures and watches. He's a lifelong fan of fine timepieces, especially those of a more historic nature - if it has a twist of Art Deco, all the better. Recent purchase: Seiko Prospex 1959 Alpinist Modern Re-Interpretation. Grail watch: Vacheron Constantin Historiques American 1921.