Lee, I sent you a couple of references on the gas planning aspects.
At the Fundies level, there really isn't that much math. You should know the tank factor on your tank, and how much in volume and psi is required for rock bottom for the proposed depth of the dive. (I cheat, honestly; I remember 40 cf for 100 feet, and 20 for 60, and use one or the other. Trying to calculate precise rock bottom for an 85 foot dive is something I can do but don't want to. If 40 cf is too much, I take a bigger tank ). Then you subtract your RB from your total gas, and divide what's left into all available, halves or thirds, depending on the dive type. Only on a "thirds" dive (rare in open water diving) would you have to worry about dissimilar tank calculations, because the very conservative assumptions you have made in calculation rock bottom, as well as the fact that you did it in volume, not pressure, will cover almost all team compositions. The exception might be if you are diving with a very new diver with really extraordinarily high gas consumption.
You memorize your tables, and remember one's from half maximal depth.
I think maybe you are making your own life too difficult.
At the Fundies level, there really isn't that much math. You should know the tank factor on your tank, and how much in volume and psi is required for rock bottom for the proposed depth of the dive. (I cheat, honestly; I remember 40 cf for 100 feet, and 20 for 60, and use one or the other. Trying to calculate precise rock bottom for an 85 foot dive is something I can do but don't want to. If 40 cf is too much, I take a bigger tank ). Then you subtract your RB from your total gas, and divide what's left into all available, halves or thirds, depending on the dive type. Only on a "thirds" dive (rare in open water diving) would you have to worry about dissimilar tank calculations, because the very conservative assumptions you have made in calculation rock bottom, as well as the fact that you did it in volume, not pressure, will cover almost all team compositions. The exception might be if you are diving with a very new diver with really extraordinarily high gas consumption.
You memorize your tables, and remember one's from half maximal depth.
I think maybe you are making your own life too difficult.