The 5139G-010 is a self-winding perpetual calendar with the ultra-thin calibre 240 movement beating away inside. The black lacquered dial helps all the information contained therein remain beautifully legible. Being perpetual the watch takes the leap years into account and therefore will not require adjusting assuming it stays wound. This particular model is unique in the sense that the case features Patek's beautiful hobnail-patterned bezel used in some time-only Calatravas. At 38mm an ideal daily companion.