jesus Glen's carrying 45% more air than I am, and we breathe down at near the same rate, PSI-wise! I gotta get some LP95's or LP108's.
I like the idea of printing that and laminating it, I think I'm gonna do that... Glen, you oughta be able to print one of those the right size and hole punch it and put it on your wrist slate.
Josh, your tank factor is 2.85. When you both fill to 3600, you have 200cf and Glen has 295cf. That's quite a difference! 67cf is your 1/3s. Considering you're using doubles, the tank factor is actually doubled. Glen's is 8.2 and yours is now 5.7. Divide 67 by Glen's 8.2 tank factor and Glen's 67cf in 108s is equal to 800psi. That means Glen must turn the dive at 2800psi. But remember, at the cavern and intro levels, you must adhere to the rule of 1/6s in doubles, not 1/3s. So you would turn at 3000 and Glen would turn at 3200.
FWIW, in the water I use a "10% rule". For every cf difference in tank size, I subtract 10psi from the turn pressure. This works for doubles. So when matching 85s and 95s. There's 10cf difference, so the diver in the 95s turns at 100psi less than the diver in 85s. IE. 85s turns at 1200 and 95s turns at 1100.
TF for double 85s = 6.4
TF for double 95s = 7.2
85s @ 3600psi carry 230cf
95s @ 3600psi carry 259cf
85s 1/3s = 76cf
95s would have to turn at 1056. Not exactly 1100, but close enough considering the inaccuracy of SPGs. I also teach that you should never dive to full 1/3s of your gas. So this rule works for me
When comparing 108s and 95s, the diver in the 108s must turn at 130 psi, rounded up to 200 psi less than the diver in 95s.
TF for double 95s = 7.2
TF for double 108s = 8.4
95s 1/3s = 86cf
108s would have to turn at 1024. 95s turn at 1200 and 108s turn at 1000.
Compare 108s and 85s and the diver in 108s turns at 300 psi less than the diver in 85s.
85s 1/3s = 76cf
108s would have to turn at 905. 85s turn at 1200 and 108s turn at 900.
It's not perfect, but it works for a quick in water calculation and works great if you don't push the limits of actually diving to 1/3s, which no one should be doing anyway.
