The main Royal Oak styles were fitted with the calibre 2121 motion, which was based on the calibre 2120 made by Audemars Piguet in 1967, the world’s thinnest self-winding motion in the period with date indication, and an All round top of three.05mm. The calibre 2121 was also Outfitted using https://www.watchesworld.com/frozen-in-time-luxury-watches-for-winter/