The Audemars Piguet Royal Oak Perpetual Calendar ref. 25654BA.OO.0944BA.01 is a rare early iteration of the perpetual calendar complication within the Royal Oak collection—crafted in 18K yellow gold and measuring 39mm in diameter. Introduced in the mid-1980s, this reference is part of the first generation of Royal Oak Perpetual Calendars, distinguished by its ultra-thin profile and open, symmetrical dial layout. The gold-toned dial features subdials for day, date, month, and moonphase, while the applied hour markers and baton hands reinforce the watch’s cohesive yellow-gold aesthetic. At just 9.3mm thick, the case houses the ultra-slim automatic calibre 2120/2800, developed in collaboration with Jaeger-LeCoultre. The integrated bracelet and octagonal bezel retain the Gerald Genta design language, while the solid caseback marks it as an earlier production model. For collectors drawn to vintage Audemars Piguet with technical depth and historical relevance, ref. 25654BA remains a compelling acquisition.