Thank you for the encouragement & the advice. I did start Adv. Nitrox first but have yet to finish it. I originally was going to do the Adv. Nitrox in rec. gear, but it proved not to be at all user friendly. My instructor recommended to me, to start using doubles. At first I really struggled with them, but am now starting to get comfortable with them. I still have some minor tweaking to do with my buoyancy control & trim, but it is coming along; just sometimes a little slower than I would like. My instructor mentioned that the cavern class would definitely help with the Adv. Nitrox, so that was one of the deciding factors for me to take the course. I do understand the reasoning behind the single tank standards though & don't necessarily disagree with that reasoning, nor do I disagree with your reasoning behind using double tanks. From what I've seen ( & I could always be mistaken), my instructor does allow for the use of double tanks in his class (unless he has reason to believe that someone would be dangerous for some reason, then he limits them) I am personally, a cautious (& I believe a careful) diver & don't knowingly dive beyond my training &/or ability without the presence of an instructor in a training environment. It looks like it may be a few months out for the class to start yet, so more time to study, practice & get even more comfortable.