This K-serial Audemars Piguet Royal Oak Double Balance Wheel Openworked Ref:15407ST.OO.1220ST.01 is rated 9.99 out of 10. The Royal Oak Double Balance wheel Openworked tackles stabilising issues by fixing a second balance wheel and balance-spring assembly on the same axis. The new patented geometry involves a very complex manufacturing procedure, but the payoff is huge: greatly improved precision and stability. It comes with box and warranty card dated in May 2019.