The Audemars Piguet Royal Oak Offshore Tourbillon Chronograph Steel Skeleton Dial 45mm Ref. 26421ST.OO.A002CA.01 demonstrates advanced engineering and openworked design. Released in 2018 for the 25th anniversary of the Royal Oak Offshore, this 45mm model is constructed from stainless steel and features a skeletonized dial that exposes the manual-winding Calibre AP 2947. The movement offers a 173-hour power reserve and integrates a 30-minute chronograph, column wheel, and visible tourbillon escapement—key technical highlights for watch enthusiasts. The transparent dial is protected by a sapphire crystal, while luminous dot markers ensure legibility. The robust case is matched with a black rubber strap and stainless steel pin buckle for secure, comfortable wear. Water resistance is rated at 100 meters. This reference stands out for its intricate openworked movement and anniversary significance, making it a notable choice for collectors seeking a high-performance tourbillon chronograph in the Royal Oak Offshore series.