Audemars Piguet Royal Oak Perpetual Calendar 38mm Smaller, Smarter Audemars Piguet has opened a significant new chapter for one of its most complicated and acclaimed timepieces, the Royal Oak Perpetual Calendar. Previously available only in a 41mm case, the Le Brassus-based manufacturer now offers it in a more compact and versatile 38mm diameter. As part of the brand's 150th anniversary...