Cave fill final gas volume
- Thread starter lunaire
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Tom_Ivan
Contributor
Why don't y'all just agree to switch to metric? 
Capt Jim Wyatt
Hanging at the 10 Foot Stop
Staff member
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Scuba Instructor
We went to the moon using Imperial, works just fine.
If you’re really into nerding out on the math, this is all a fun exercise. However, practically, temperature and SPG inaccuracy will have a bigger impact than z factors and all of that. Easier and less room for human error if you just use rounded tank factors so you can do the math quickly in your head on the fly. No need to measure with a micrometer if we’re chopping with an axe.
Not precisely an answer to the original posting question. Not precisely.
But this is a table (a triplicate copy of the same table) I laminate and give to my students which fits in a wetnotes.
I made it because I suck at math - and don't trust my ability to, say, divide or multiply by 7 in my head on the fly - but value dissimilar tank gas matching.
The left columns, obviously, are tank sizes and tank factors. The top row is useable pressure when figuring thirds. The main grid is all volumes in cubic footage. The idea is once you've figured out who the limiting factor is you've got their usable pressure which, by simple triangulation, you've got their useable volume. Then you find the closest volume in whatever tanks other team members are diving and find what pressure that volume is in their tanks and you've got their useable pressures, too.
If, for whatever reason, you need a total fill volume at triple those useable pressures/volumes... just multiply by 3? (I'd probably still need a calculator.)
But this is a table (a triplicate copy of the same table) I laminate and give to my students which fits in a wetnotes.
I made it because I suck at math - and don't trust my ability to, say, divide or multiply by 7 in my head on the fly - but value dissimilar tank gas matching.
The left columns, obviously, are tank sizes and tank factors. The top row is useable pressure when figuring thirds. The main grid is all volumes in cubic footage. The idea is once you've figured out who the limiting factor is you've got their usable pressure which, by simple triangulation, you've got their useable volume. Then you find the closest volume in whatever tanks other team members are diving and find what pressure that volume is in their tanks and you've got their useable pressures, too.
If, for whatever reason, you need a total fill volume at triple those useable pressures/volumes... just multiply by 3? (I'd probably still need a calculator.)
Use the “M” factor, a given tank rated at 2650 psi filled to 3400 has “M”ore air, dive accordingly. 
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