The Audemars Piguet Quantieme Perpetuel 5548BA is one of the most historically important automatic perpetual calendars Audemars Piguet has ever produced. When the 5548 debuted in 1978, it was the world's thinnest automatic perpetual calendar wristwatch, an achievement made possible by the Caliber 2120/2 ultra-thin self-winding movement developed in collaboration between Jaeger-LeCoultre, Audemars Piguet, Patek Philippe, and Vacheron Constantin in the late 1960s. The 5548BA carries that movement in an 18k yellow gold dress case under 8mm thick, with the slim bezel and refined dauphine hands that defined late-1970s and early-1980s Genevan dress watchmaking. The silvered dial carries the full perpetual calendar program in four sub-dials, displaying day of the week, date, month with leap-year indicator, and moon phase, with the calendar correctly tracking through century-end exceptions until 2100 without manual adjustment. The Caliber 2120/2 beats through 38 jewels with the patented beryllium-rail full-rotor system that remains, decades later, one of the thinnest full-rotor automatic architectures ever produced in serial wristwatch production. Financing options available — contact us for details. Pre-owned.