Audemars Piguet Royal Oak Men’s Watch 41MM Black Stainless Steel 15500ST. 60 m (6 ATM). The next evolution of the Ref. 15450 Self-winding Royal Oak comes in the 15500 form, which was introduced at the SIHH 2019. The most significant update to the Self-winding models is the in-house movement, which for the 15500ST. 03 is the self-winding caliber 4302 that has date functionality and a power reserve of 70 hours.