Audemars Piguet Royal Oak Perpetual Calendar Ultra-Thin Watch
It's funny that the world's thinnest perpetual calendar might have the longest name. Based on Audemars Piguet's RD#2 concept, the 41mm, titanium and platinum case of the Royal Oak Perpetual Calendar Ultra-Thin is just 6.3mm thick. The Calibre 5133 movement that powers it is just 2.89mm thick, so as to make room for the satin blue dial with white gold markers, lumed white gold hands, and the various sub-dials indicating the day, date, astronomical moon, month, leap year, and day/night. It's finished with a matching titanium bracelet and is available exclusively at Audemars Piguet boutiques.