This Audemars Piguet Quantieme Perpetual Calendar reference 25548PT is one of the watches that fixed the modern perpetual calendar in place. Its self-winding movement carries a perpetual calendar with moonphase, the configuration that made this line such a decisive part of Audemars Piguet's late twentieth-century output. In platinum, the case measures 36.5mm across and 7.7mm thick, a set of proportions that keeps the watch notably elegant on the wrist. The silver dial suits the restraint of the reference, letting the calendar display remain balanced rather than crowded. Audemars Piguet treated the ultra-thin perpetual calendar as a serious house specialty, and this watch sits near the beginning of that long arc. For a collector drawn to the period when complicated watchmaking turned back toward classical proportion, the 25548PT remains a remarkably complete statement of that shift.