Classic (non-Royal Oak) 5548

Round perpetual calendarPerpetual calendarA calendar mechanism that accounts for different month lengths and leap years. designed by Jacqueline Dimier around calibreCaliberThe designation of a watch movement, identifying its design or movement family. 2120/2800, then the world’s thinnest automaticAutomaticA mechanical movement wound by a rotor as the watch moves on the wrist. perpetual calendarPerpetual calendarA calendar mechanism that accounts for different month lengths and leap years.. Its success in the quartz crisis led to the Royal Oak QP and helped revive traditional complications. Renamed 25548 with AP’s switch to five-digit references in 1984–85.