Royal Oak models, a revolutionary luxury sports watch launched in 1972. This timepiece reference 15500 is one of the newest iterations of the iconic Royal Oak model, replacing reference 15400. Boasting an elegant 41 millimeter case, it houses the new in-house caliber 4302. Compared to its predecessor, the new caliber most notably has a longer power reserve function. Compared to the caliber 3120 which provided 60 hours, this version provides 70 hours.