It is the Portuguese watch which one might easily have imagined on the wrist of famous seafarers. Learned individuals with the necessary far-sightedness, spirit of discovery and a concrete vision of the future. Because the future is precisely the area of expertise of this particular time machine, which is as beguiling as it is technically impressive. The perpetual calendar, invented 25 years ago, lives on here in all its original complexity and genius – in conjunction with an IWC-manufactured large movement from the 50000-calibre family with a seven-day power reserve.

This is an ideal combination for a complicated watch with calendar indications displaying the date, day, month, year in four digits and perpetual moon phase. The watch displays advance completely autonomously, mechanically programmed and synchronized with one another. Save for a leap day correction that becomes necessary in February 2100, this continues uninterrupted and without any intervention on the part of the wearer, who simply needs to input the required kinetic energy via the highly efficient Pellaton winding system of the automatic movement when wearing the watch. According to the complicated Gregorian calendar, which always assures years of almost constant length, the leap day that would be due to occur is absent at the end of February in the year in question, 2100, and this will necessitate an adjustment by a watchmaker. It might thus be appropriate to ensure that one’s grandson or great-grandson is aware of this fact. In that far-off year, incidentally, the century slide at the end of a long transmission chain will also be advanced by a couple of millimetres, and the numeral “21” for the next hundred years set in the display window in place of the currently indicated “20” to make the year display complete.

The beguiling new eternity in the form of the Portuguese Perpetual Calendar retains its two familiar faces: one model of this watch is equipped with a quasi-universal hemisphere lunar display (Ref. 5021), in which the miniature model of the Earth’s satellite is pictured twice. Exactly as the phases of the moon appear when viewed from the northern or southern hemisphere – that is to say reversed. This distinctive optical feature has to do with the visual angle and the different point of observation. The number of days remaining until the next full moon can also be read precisely on a supplementary countdown scale in this model. The new Portuguese Perpetual Calendar in 18 carat red gold with hemisphere lunar display (Ref. 5021) differs from the previous rose gold model through the rather warmer hue of the case material. The second new model, the white gold variant with a midnight blue dial and silver-plated highlights, for example for the seconds subdial or on the moon disc, presents a particularly attractive side as regards colour. The simultaneous display of the two moons functions as follows: it is not the moon disc itself that moves, but an engraved disc representing the globe with two circular cut-outs set against a silver-coloured background, which carries two blue circular surfaces in a horizontal plane. In this way, the moon in the southern hemisphere is shown mirror-inverted or laterally reversed in relation to the moon in the northern hemisphere.

A second version of the Portuguese Perpetual Calendar is available with the classic cut-out moon phase display when observed from the northern hemisphere (Ref. 5023). The Earth’s satellite waxes onto this miniature stage from the left behind the semicircular setting becomes visible in the middle as a full moon and wanes on the right side behind the second semicircle. It is accompanied on the moon disc by small raised stars. The two new models with the representation of the moon behind a setting are now also housed in the 44.2-millimetre case of their sibling models (Ref. 5021). These are the variant in18carat red gold with a silver-plated dial, solid red gold appliqués and a red gold-plated moon surrounded by small stars, and a highly discreet model in18carat white gold with rhodium-plated appliqués and a slate-coloured dial.

As far as the key astronomical indication of the Portuguese Perpetual Calendar, the moon, is concerned, it is able to match the precision of scientific instruments: in these watch models – and in these alone – the gearing has been modified, thanks to the available space, so as to permit the moon cycle to be displayed with unprecedented accuracy. A tiny residual error of 12 seconds per lunar period (29 days,12 hours, 44 minutes and 3 seconds) will add up to a deviation of just one day after 577 years. In other words: only the moon in the heavens is more accurate according to our current state of knowledge. And then only by a small margin.