VeniVidi:
You raised a valid point, although I have not mentioned overhead environment, so far. But taking into consideration that the DIR diving emerged from cave diving, it is a valid point.
Ok. Let me first define what -I- treat as overhead, since it's possible that we aren't on the same page here. Overhead, IMHO, is -any- dive where a direct, no stop, ascent to the surface isn't a viable option. Wether it be true hard overhead, deco, a lack of desire to free ascent away from a line, whatever...
So in other words, I treat most of my dives as overhead dives, even if I'm within recreational depths and times, because I'm not gonna be 'that guy' that comes up 500 feet from the boat!
Only, who or what tells you that you stay cool if a calmity occurs? I know, a lot can be anticipated by schooling and training - my thought just circle around the residual risk of irrational behavior pattern by unvoluntary emotional overcomes. And I am convinced that any person has his/her personal stress threshold. So why not anticipate?
Well, for one feel experience is far more important than training, and while training is necessary, it doesn't replace the need to work your way up to those new limits that you've been trained for. With experience comes confidence; as things happen you judge your reaction to them and make a call in post dive analysis if you were within your personal limits, close to them, or over them.
I used to calculate my SAC rate for every dive. I don't do this anymore because I know during the dive if it's on what I expect or not. If I'm doing very well or very bad, I'll calculate it out, to make sure I don't have to adjust the numbers I use for my planning, but in general I -know- my SAC rate. If my SAC rate is running high, it's due to some sort of stress... then I look really close to those dives and look for explinations for the high gas use.
Personally I have shown myself I have some ability to stop and relax. I believe it was dive #64 where I thought I was the balls, coming back from some 100+ foot wreck diving in North Carolina and heading out for some deep stuff off New York. I was down at 121, in cold dark water, when my backup reg started to bubble and I got slammed with the dark narc. I thumbed it and my buddies waved 'goodbye'. I started heading back to the line when the voice came... you know the voice.... the one in the back of your head. "You're gonna die!". On the verge of panic I stopped, checked my gas, checked my reel, checked my liftbag, checked my time. "Whatever brain-dude.. I can ascend any time I want". Got my breathing back in control and continued on. Got to the line, checked gas and time. 12 minutes, 1200 psi... which was precisely my plan limits.
I learned a -lot- from that dive. About myself, about buddies, about limits, about arrogance, about complacency, about limits, about limits, about limits.... You get the point.
So anyway... back to the question at hand. First off think about that second pressure guage. Is it necessary to your ability to keep cool? I mean, is it -really-? Can you truely believe that the information is going to be enough to keep you cool in a stressful situation? I'm going to go out on a limb and guess "no". But just because I believe that, doesn't mean you believe that.... YET.
Now the catch is that you truely need to use your SPG as it's should be used; as a backup guage to tell you your left post is on, your isolator is open, and you aren't overly stressed and need to cut back on your dive plan. But that's a leap of faith that takes experience to accept.
So, if you're actually still reading my babble at this point, I'm gonna give you a piece of advice. I'm not gonna tell you to dump your second guage. Keep it. But: For now on, don't look at your SPG to get a number, get a number then look at your SPG to see how it compares. Don't worry about it at first... just guess what you think it should be. You'll be amazed at how fast you start to nail it. After a while you'll notice you subconciously take your mental comfort into account too.... where your 'guesstimate' starts to take into account a nice easy drifting dive, vs. a dark, cold, motoring against current dive.
If you do that, you'll eventually realize that you are using your SPG as a backup, using your brain as the primary, and you'll have the confidence to accept that if somethings gonna happen to take you over the edge, that second pressure guage ain't gonna help you, and really was just a crutch.
