Actually NAUI's Master Scuba Diver is a specific class that is 23 hours of academics and 8 dives including Emergency/Rescue, Deep/SimDeco, LimVis/Night, Nav, Search/Recovery, + 3 elective dives. Naui rescue is a separate class that Master does not actually require, though Naui requires rescue skills from OW on, and Master requires AOW. Master was apparently meant as all the leadership content except the leading/teaching parts. (Though except the stand alone rescue class itself; and some personal water skills have been harder in DM than Master. Master, rescue, and now leadership prep FIT, are prerequisites for AI/DM, plus Nitrox, O2, and professional diver first aid)