This Audemars Piguet Royal Oak reference 5402ST is the original Jumbo, and the A-series run sits closest to the model's starting point. For a collector who wants the Royal Oak before later revisions took hold, that early series is the natural place to look. Its self-winding caliber 2121 is the ultra-thin movement that helped define the reference, with a suspended rotor construction that kept the watch remarkably slim for its kind. In stainless steel, the case measures 39mm across and 7.1mm thick, proportions that still make the 5402ST wear flatter and leaner than most sports watches that followed it. The black dial gives this example a quieter look than the blue version more often associated with the reference. Audemars Piguet did not simply launch a successful model here; it established the design language that turned the luxury steel sports watch into a category of its own. This Royal Oak was just fully serviced by Audemars Piguet in Q3/2026.