which I never had the pleasure to handle. Something I have to work on ;-)
The reference 5104 Grand Complication in platinum with a minute repeater and a perpetual calendar with a retrograde date indicates the date and the moon age, as well as the day of the week, the month, and the leap-year cycle in an unprecedented way. Patek Philippe developed and patented an ingenious system that relies on small sapphirecrystal wafers for the calendar displays, resulting in a largely transparent dial which reveals the remarkable perpetual calendar mechanism.
Each of the three moving sapphire-crystal disks is underlaid with a small black rectangle that provides a contrasting background for the white day, month, and year indications.