IWC Schaffhausen Portugieser Eternal Calendar
Unveiled at the Watches and Wonders Geneva 2024 luxury watch fair, the new Portugieser Eternal Calendar by IWC Schaffhausen incorporates an advanced perpetual calendar mechanism and a moon phase function with an accuracy of 45 million years.
Dressed in a platinum case, the Portugieser Eternal Calendar (Reference IW505701) is the first secular perpetual calendar watch made by IWC. In addition to recognising the different lengths of the months and adding a leap day every four years, this timepiece also takes into account the Gregorian calendar’s complex leap-year exception rules.
A newly engineered 400-years gear ensures that the calendar automatically skips three leap years over four centuries – an event which will occur for the first time in the year 2100. Another key feature of this watch is the extremely precise moon phase display. Thanks to a newly developed reduction gear, the Double Moon™ phase display will only deviate from the moon’s orbit by one day after 45 million years.
Translating the irregular calendar into a mechanical program for a wristwatch remains one of the most challenging engineering feats in fine watchmaking. The Gregorian calendar, which is used across most continents and cultures today, divides the year into twelve months with 28, 30 or 31 days. Years that are divisible by four count as leap years, meaning that a 29th day must be added at the end of February.
However, an additional correction is needed to keep the calendar in sync with the actual solar year: only those centurial years that can be divided by 400 are leap years, all others are common years. This means that 2000 and 2400 are leap years, while 2100, 2200 and 2300, for example, are common years. A traditional perpetual calendar, however, is only programmed for a four-year cycle, in which three common years are always followed by a leap year.
By design, it will interpret the year 2100 as a leap year and need a correction. The same will happen again in 2200 and 2300. As a result, a perpetual calendar will need three corrections over a period of 400 years.
A secular perpetual calendar like the Portugieser Eternal Calendar (Ref. IW505701), on the other hand, is mechanically programmed to take these complex nuances into account. It will calculate the leap year correctly until at least the year 3999, as it has not yet been officially decided whether the year 4000 will be a leap year or not.
The Portugieser Eternal Calendar is based on the same modular and synchronised design as the existing perpetual calendar. All its displays can be advanced using the crown.
However, while the perpetual calendar is programmed for a four-year cycle, the Portugieser Eternal Calendar features an additional mechanism. Every four years at the end of February, a new module informs the calendar about whether the leap year takes place or not. This so-called 400-years gear completes only one revolution every four centuries.
It contains three indentations, which cause the calendar to skip three leap years over that period. This module is designed with impressive efficiency and technical elegance and consists of only eight parts, underscoring IWC Schaffhausen’s engineering approach to fine watchmaking.
Since the introduction of the perpetual calendar almost four decades ago, IWC has also taken great strides to continuously improve the accuracy of its moon phase displays.
While the Da Vinci Perpetual Calendar Chronograph (Reference IW3750) from 1985 featured a moon phase precision of 122 years, the first Portugieser Perpetual Calendar (Reference IW5021) from 2003 impressed with a moon phase accuracy of 577.5 years.
IWC’s engineers have now taken on the challenge to develop a new moon phase display with unprecedented precision.
The difficulty in displaying the moon phase on the dial of a watch lies in the fact that the moon does not follow a daily rhythm in its orbit around the Earth. A cycle from new moon to new moon – one lunation – does not last 30 days, but rather 29 days, 12 hours, 44 minutes, and 2.88 seconds. The duration of one calendar month must therefore be reduced as close as possible to one lunar cycle.
This is achieved by placing a reduction gear between the base movement and the moon phase disc. The key to high precision lies in the quantity of wheels used, their proportions and the number of teeth they have. IWC’s engineers have now used a special computer program to simulate more than 22 trillion different combinations.
For the Portugieser Eternal Calendar, they came up with a new reduction gear train using three intermediate wheels. Mathematically, the display will only deviate from the moon’s orbit by one day after 45 million years. Another challenge consisted in integrating this new gear train into the confined space of the eternal calendar module.
The moon phase is displayed on the dial using the characteristic Double Moon™ indication, which shows the moon as seen from the Northern and Southern hemispheres.
The display consists of two superimposed discs. A celestial disc with two small circular openings rotates above an immobile lower disc with two dots. This negative representation gives the impression that two small moons are waxing or waning. Here, the lower disc is made of titanium and decorated with a Guilloché pattern. The upper disc is made of glass.
The Portugieser Eternal Calendar features an intricately finished platinum case with polished and brushed surfaces. Another highlight is the glass dial, which is manufactured in a complex process. In the first step, the underside of the dial is frosted and lacquered in white.
The subdials are machined and polished separately and subsequently fixed onto the dial. In the next step, the printing is applied, and the appliques are mounted by hand. The depth of the glass lends the print and appliques a floaty lightness.
The numerals and the characteristic Portugieser minute scale are printed on a white lacquered flange sitting between the glass dial and the front glass. The box-glass sapphire crystals are machined and polished in an elaborate process.
Inside the 44.4 mm diameter platinum case beats the newly developed IWC-manufactured 52640 calibre.
The high-end mechanical self-winding perpetual calendar movement features a highly efficient Pellaton winding system. Equipped with a bidirectional rotor and two mainspring barrels, it builds up a power reserve of seven days (168 hours).
Parts of the winding system that are subject to extremely high stresses are manufactured using virtually wear-free zirconium oxide ceramic. The movement has been elaborately finished with circular graining and Geneva stripes and can be admired through the box-shaped sapphire glass case back.
The IWC Portugieser Eternal Calendar watch is fitted with a black alligator leather strap from the Italian leather artisan Santoni with a platinum folding clasp.
Model: IWC Portugieser Eternal Calendar, Reference IW505701
Movement
IWC-manufactured automatic calibre 52640
Pellaton automatic winding system
Frequency: 28,800 vph / 4 Hz
Jewels: 54
Rotor in 18-carat gold
Power reserve: 7 days (168 h)
Functions
Power reserve display
Secular perpetual calendar with displays for the date, day, month, year in four digits
Perpetual moon phase with 45,000,000 years accuracy for both northern and southern hemispheres
400-years gear for the recognition of irregular leap years
Small hacking seconds
Case
Platinum case
Diameter: 44.4 mm
Height: 15 mm
Glass: Sapphire, double box-glass, antireflective coating on both sides
See-through sapphire glass back
Water-resistance: 5 bar
Dial
Glass dial with white lacquer, rhodium-plated hands and appliqués
Strap
Black alligator leather strap from Santoni
Platinum folding clasp
