This Patek Philippe 3940J is a first-series example of one of the maison's most revered perpetual calendars, a reference released during the Quartz Crisis as a statement of Patek Philippe's unwavering commitment to mechanical high horology. First-series pieces are distinguished by their sunken subsidiary dials and the earlier, smaller signature, details prized by collectors seeking the purest early execution of the model. Powered by the automatic calibre 240 Q with its ultra-thin micro-rotor, it displays a full perpetual calendar with moon phases and leap-year indication across a beautifully balanced three-subdial layout. The yellow-gold case measures 36mm across and just 8.8mm in thickness, a remarkably slim profile that lets a grand complication wear with everyday ease. A silver dial gives the composition clarity and understated elegance. An enduring benchmark of Patek Philippe's mastery of the perpetual calendar.