The Portuguese Perpetual Calendar

April 2003

Launched 70 years ago and re-introduced 10 years ago, IWC's Portuguese is now one of the world's watch classics. The new Perpetual Calendar also looks destined for greatness.

The new Portuguese Perpetual Calendar watch combines IWC's own 5000 calibre movement with the perpetual calendar and an entirely new moon phase display that has been patented by the company.

The basis for the drive is the same large IWC automatic movement, with its famous Pellaton winding mechanism (invented by Albert Pellaton the company's Technical Director from 1944 to 1966) and the seven-day power reserve and date, that is used in the Big Pilot's Watch. Added to this is a perpetual calendar module that is an integral part of the Da Vinci family of watches and the GST Perpetual Calendar. However, the difference is that the Da Vinci system has 82 pieces and the Portuguese has 109.

The calendar functions are almost identical with those of the aforementioned models. The mechanisms have been increased in line with the larger Portuguese automatic movement. This also has a positive influence on the readability of the individual displays. Three hands tell the wearer the date (at 3 o'clock), day (at 9 o'clock) and month (at 6 o'clock), and there is a four-digit year display in a window between 7 and 8 o'clock.

A new Moon Phase
The Portuguese houses an entirely new representation of the moon phase, which now shows the position of the moon in both the northern and southern hemispheres. This innovative display is made possible using a disc with two opposing circular windows which rotate above a yellow surface with two black circular areas of identical size lying in the horizontal plane. The result is two moon phase displays, which are not situated at a single fixed point, but are constantly in motion. Above the centre, the position of the moon can be seen as it appears to an observer in the night sky of the northern hemisphere, and below the centre, inhabitants of the southern hemisphere can find a true representation of the moon's position.

Astronomers have calculated that the moon requires precisely 29 days, 12 hours, 44 minutes and 3 seconds for one complete orbit of the earth. The moon disc in the majority of wristwatches has 59 teeth and two moons situated opposite one another. A watch of this kind accordingly takes precisely 29 days and 12 hours to complete a moon phase. The deviation of plus 44 minutes and 3 seconds adds up to one day over 32 months and should then be reset, usually with the help of a correction button. IWC has dispensed with this and the perpetual calendar is operated via the crown. Anyone inheriting a Portuguese Perpetual Calendar will only need to visit a watchmaker after 577 years to have the moon phase display corrected since it loses only one day during that period of time.

200-hour power reserve
The 5011 calibre has a power reserve of more than 200 hours (due to an extra-long mainspring) and the perpetual calendar uses very little of this power. Nevertheless, the self-contained power Portuguese Perpetual Calendar reserve was restricted to 168 hours - or seven days - to avoid a fall-off in energy towards the end of the spring force curve and to maintain the escapement accuracy as constant as possible for the entire period. The necessary accuracy is also taken care of by, among other things, the escapement regulator with a screw balance, two adjusting snails and a Breguet balance spring borrowed from the legendary Pilot's Watch Mark XI.

The movement is fully wound after exactly 1960 rotations of the rotor and this is indicated externally on the power reserve display at 3 o'clock. The date display is also in this position in the calendar module, and both displays work concentrically.

The remaining power reserve is indicated in the inner ring by a short hand, and the date can be read in the outer ring.

Because of the large diameter of the watch - 44 mm, all the displays have been made larger. There is a sapphire crystal front and back and the watch is water-resistant to 30 metres.

As one would expect from what must surely be a future classic, the timepiece not only looks good, but also it is very user-friendly.