IWC Portuguese Chrono-Rattrapante Open Caseback (IW3712-07)

We already introduced you the Portuguese Annual Calendar and the Portuguese Yacht Club Chronograph. Today we are presenting the Portuguese Perpetual Calendar with a double moon (Ref.5034) and the Portuguese Perpetual Calendar with a single moon (Ref.5033).

The perpetual moon phase display is one of the Schaffhausen manufacturer in-house designs, primarily for a level of precision unique in a mechanical wristwatch. It takes the moon 29 days, 12 hours, 44 minutesand 3 seconds to orbit the earth. Kurt Klaus, the master watchmaker at IWC who designed the company's first perpetual calendar, succeeded in the mid-1980s in reducing the deviation of the mini-moon of the display compared to the moon's actual orbit to just 1 day in 122 years. It was a surpassed only in 2003 with the introduction of the large 5000 calibre. Thanks to its considerable size, the calibre's larger moon phase wheels have a higher transmission ratio. As a result, the display will need to be corrected by 1 day only after 577.5 years.

In the Portuguese Perpetual Calendar with the double moon (Ref. 5034), the moon phase and its mirror image show the state of the moon in both the northern and southern hemispheres. For the first time, the model no longer features the countdown display that shows the number of days remaining until the next full moon. Instead, the watch designers have transformed the subdial with the double moon display into a star-studded night sky the same colour as the large dial, so that the moon and stars appear to hover in infinite space. A further new feature of the design is the introduction of the railway-track-style chapter ring typical of the Portuguese, which puts the model closer in appearance to the classic original. The dial appears more balanced and elegant because the subdials for the date and week are also the same colour. No visible changes have been made to the model with a single moon (Ref. 5033) with the exception of several minimal design modifications. However, the new arched-edge front glass reduces the optical height of the case.

The perpetual calendar shows not only the lunar cycles but also the seconds, minutes, hours, date, day, month and year in four digits. Mechanically programmed, the calendar takes into account the different lengths of the months and even the leap years. Nevertheless, every 100 years (2100, 2200 etc.) a leap day that would normally be due is omitted, which means that a watchmaker will have to advance the calendar on 1 March. Another intervention will be necessary in 2300 in order to replace the current century slide, which bears the numbers 20, 21 and 22, with a new one for the years 2200 to 2499.

Both models feature in-house movements from the new IWC 52000-calibre family. Two barrels supply the power needed to provide 7 days' running time and to drive nine functions and displays. The bidirectional Pellaton winding mechanism with its new ceramic pawls is extremely efficient. A glance through the see-through sapphire-glass back reveals the sophisticated design of the IWC-manufactured 52610 (Ref. 5033) and 52615 (Ref. 5034) movements.

The Portuguese Perpetual Calendar with a single moon is available in two versions: in an 18-carat white gold case (Ref. IW503301) with a slate-coloured dial and in an 18-carat red gold case (Ref. IW503302) with a silver-plated dial and a red gold-plated moon against a midnight blue background. The Portuguese Perpetual Calendar with a double moon is likewise available in an 18-carat white gold case (Ref. IW503401) but with a midnight blue dial. The 18-carat red gold model (Ref. IW503404) with moon phase displays for the northern and southern hemispheres is fitted with a slate-coloured dial. Both watches are fitted Santoni alligator leather straps.