The changes have not been devoid of reason... For example, my original
Scuba Diver course included deco as just part of the dive tables; there were lots of harrassment drills, pushups with a tank on, buddy breathing, underwater distance swimming to your gear and putting it on, etc., etc. Using hang tanks for low on air/out of air was SOP.
Much of this stuff really serves no useful purpose as skills needed by the recreational scuba diver. But here is just a partial list of things not taught back then, mostly because they didn't exist:
Using an octopus
Using a SPG
Using a BC
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One skill that has been abandoned that I think should be an essential tool for every diver is tank valve manipulation underwater. I also feel the basic watermanship requirements are overly weak now.
Rick