Analogue date displays with hands have a long tradition in IWC watches featuring perpetual calendars. In the case of the Portuguese Perpetual Calendar, for instance, the date, day and month are to be found on three subdials and, thanks to the clear layout, are extremely easy to read.
The classic moon phase display with discs is usually found at “12 o’clock”. The Ingenieur Constant-Force Tourbillon is one exception and displays the double moon at approximately “1 o’clock”. The moon phase display used in the Portuguese Grande Complication is astonishingly accurate and deviates by just 0.002 per cent, or 1 day, in 122 years. The Portuguese Perpetual Calendar is even more precise. Larger moon phase wheels with a higher number of teeth reduce the deviation so drastically that a future inheritor of the watch would theoretically need to take it to a watchmaker to have the moon phase display adjusted by only 1 day in 577.5 years.
