The Audemars Piguet Royal Oak Selfwinding Blue Topaz “50ᵀᴴ Anniversary” 37mm (ref. 15554BC.TO.1274BC.01) is an automatic sport watch, with a 37mm 18-carat white gold case, powered by the 5909 movement and a 60-hour power reserve. Water resistance is rated to 20m, under a sapphire crystal.