The Royal Oak Selfwinding Perpetual Calendar Ultra-Thin, the world’s thinnest automatic perpetual calendar wristwatch, marks Audemars Piguet’s latest technological milestone with a movement of 2.89mm thick and a case of 6.3mm in height. Presented as a prototype at the SIHH in 2018 as RD#2, it now combines titanium and 950 platinum for an elegant look and a lighter feel on the wrist.