Audemars Piguet Royal Oak Double Balance Wheel Openworkedl Royal Oak Double Skeleton Rocker tackles these stability problems by fixing a second balance-spiral group on the same axis. The new patent-pending Dualbalance structure involves an extremely complex production procedure, however, with an excellent result: a marked improvement in precision and stability. Steel case, glass and sapphire crystal case back with anti-reflective treatment, screwed crown.