The Audemars Piguet Royal Oak Extra Thin Yellow Gold still measures 39mm in diameter and 8.1mm in thickness. The “tank tread” bracelet is identical to the other 15202 versions. In terms of movement, these new yellow gold models are equipped with the renowned ultra-thin selfwinding Manufacture caliber 2121, first introduced half a century ago. This 3.05mm thick engine is perfectly decorated, as you can see through the sapphire crystal. Only the time (hours and minutes) and the date are displayed, as in the early Royal Oak models.