What I do take issue with is that there is a school of thought that argues that if you don't know the formulae inside out then you shouldn't be using them in the first place. Although this is most definitely true for technical divers where knowing the numbers backwards or not is literally the difference between life and death, it is not necessarily true for the recreational diver who form the vast majority of divers in the water today. To the latter group, knowing the formulae is in fact covered in their training of course. However, it seems to stop there. In practice, understanding the meaning of the result is more important than how it is derived when it comes to actually diving.
Most recreational divers, myself included, know the basic science behind Boyle's and Dalton's Laws from our early school days when science was not a separate subject. By now, most divers know how these laws apply to diving. What most of us don't do is apply these rules BEFORE EVERY DIVE. We are content to follow the instructor, apply the rule of third and turn around when we've reached that limit. It's only back on-shore, when filling out our log books that we turn our attention to what the numbers tell us about the dive that just happened. The reason we do that is because too much of the dive plan is structured around, where we are going and what we can expect to see. Very little time is spent on planning our GAS consumption and what it means at the depth we are going to dive to.
Without understanding what it means to do so, we then bundle all emergency requirements into one third of our available GAS and a third for the way back, without knowing before hand how much GAS we actually consume or needed. We feel intimidated by the numbers because we probably had a rough time in the classroom with them. So we simply trust that the leader of the dive has worked all this out for us all in a magic formula where one size fits all, when it clearly doesn't. In most cases the instructor does do this, contentiously applying extravagant and wasteful margins. As a result, the dive in fact ends up being uneventful in that respect. For, is it not after all (dangerously) true that any dive you return from safely is a safe dive?
I know of at least twenty of my dives where the dive leader had not worked the numbers, couldn't work the numbers, didn't want to work the numbers or couldn't be bothered. The result was the risk of an out of air scenario that usually ended in a premature end to the dive. In one case I went to the safety stop knowingly low on air just to experience an out of air scenario and practice my emergency procedures in a controlled manner. At its worst, the lack of GAS planning resulting in an out of air scenario was so traumatic for one member of our "fun" diving group that she gave up diving altogether and has never been back in the water since. If there is one platitude that is worth iterating it is that there is NO excuse for running out of air.
So what is it about these numbers that turns recreational divers off? The elitism associated with getting to the result that is almost certainly a turn-off when all you want to do is jump into the water and enjoy the sport. A boat that is pitching and rolling, is not the time or place to contemplate MOD, SAC and RMV. Does a recreational diver need to know what these values tell her or him about their diving before he or she gets into the water? Most certainly. Noah built the ark before the deluge, not after it. Therefore, GAS planning should all have been done before the dive, in the comfort of a chair. "Plan the dive and dive the plan" is a much over-used phrase in the diving community. Regrettably, because the planning does not include the math involved with GAS planning, in most cases divers deliberately avoid it.
At it's simplest, most of us know how to calculate pressure for any given depth in our heads. But most of us don't care to consider the importance of that single number is to determining at least 5 other factors that affect us in diving. It is as important as the "m" is in "E = mc2". At the other end of the scale, calculating our own personal SAC rate is a reasonably complicated math exercise that you don't want to be doing under pressure and two minutes before the dive. The point is not whether or not you know how to calculate these numbers. The point is whether or not you know what the results mean to you personally, whether or not you actually use the result in your dive planning often enough to tell you something about the dive you are about to embark on.
Most of us use the rule of thirds to "plan" our dive. That is however such a vague concept that it's useless in the water because it is reactive rather than predictive. Is it not better to get into the water knowing how long into the dive you will have used up your third of GAS, marking the turning point of your dive, rather than have used a third of your GAS in the middle of your dive only to find that the rest of the group has not and then you have to split away from the group with a valuable resource to the group or worse have everyone end their dive because of you or even worse you keep going and endanger yourself because you are too embarrassed to call the dive? So what is important at this point: how you calculated SAC or what SAC predicted?
If we democratize the math involved in diving and focus on the meaning of the result, we take away the elitism from the numbers and place a powerful tool of dive planning in the hands of the majority. If we do that, then we not only give ourselves a level of comfort with our diving, but we also make ourselves better divers. The two side effects of this strategy are compelling and hard to ignore. The first is that any proactive planning relaxes the diver in the water giving them more time to enjoy the reason why they got into the water. The second is that it gives them mastery over the numbers rather than the other way around. Both have the natural effect of building confidence that is not just the realm of an elite few in their pursuit of perfection.
So take your diving to the next level. Certainly, learn the constructs of the formulae. Don't stop there however. Once learned ditch the pen, paper and slide rule. Replace them with tools that allow you to focus more on the results in your dive's GAS planning than you ever would have. That is to say use it or loose it. Is it not after all better to come back safely with wasted air left in the tank than unsafely with nothing in the tank at all?
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