The main Royal Oak types were fitted with the calibre 2121 movement, which was depending on the calibre 2120 created by Audemars Piguet in 1967, the planet’s thinnest self-winding movement in the period with day indicator, and an General height of 3.05mm. The calibre 2121 was also Geared up using https://www.watchesworld.com/frozen-in-time-luxury-watches-for-winter/