When I took my initial Scuba course, there were essentially two ratings - Diver and Instructor. When I re-entered the formal training arena some 24 years later, the shop owner I was doing business with recommended I take the "Advanced" NAUI course. It was interesting... aside from the equipment changes and additions (those were not trivial, as they included SPGs and BCs
), I was surprised that the physics, physiology, dive tables and actual diving skills - and especially the physical fitness - required were somewhat less than my original YMCA diver course.
I was also surprised to learn that I was the only one in the class who could really work the tables backwards & forwards and the only one who had been introduced to staged decompression in the original diver course. (of course we knew nothing of redundancy beyond hang bottles, etc., so it was an entirely different world from today's "tech" diving - but we did cover basic deco in the original course. It was just looked at as a "normal" extension of the tables; what you did when you needed to do it, rather than a "beyond the realm of basic diving" thing).
Bottom line: I had expected much more "meat" in an "Advanced" diver course, but found that except for equipment changes it was the NAUI "Master Diver" course that was best equated to my original diver course (but still without deco). Now I have no idea how much of that can be attributed to changing standards and how much to my original instructor (ex Navy diver), but I do know that today's courses spread what I learned in that original course over the OW - Advanced - Rescue - Master Diver steps, at least in the physics/physiology/emergency/skills areas.
For an even more dramatic comparison, one can look at Rutkowski's original Nitrox course compared to today's offerings.
Rick