seems a bit complex...
All you really need is average depth + total time, SAC in ft3/min (this is tank independant and why I NEVER try to figure SAC in PSI).
(depth/33)+1 = ATA
ATA*SAC*minutes = approximate gas usage in ft3
in metric I suppose it would be something like SAC in Ltr3/min and the equation is:
(depth/10)+1 = ATA
ATA*SAC*minutes = approximate gas usage in Ltr3
The only reason to list any info about the tank at all is maybe to put up an alert if the tank isn't big enough to contain the gas you will need for the dive being planned?
Remember, unless you are planning for a robot to be diving the tank instead of a human, the real-world numbers will never be exact because so many things can affect breathing rates +/- from dive to dive.
Working out a good estimate (with maybe a bit of round-up fudge factor thrown in) is the best way to go IMHO. figuring it out down to the last PSI isn't all that usefull cause the shop may overfill or underfill a bit on any given visit due to ambient temperature and how busy they were that day (fast fill speeds heats up tanks causing short-fills), etc...
It's REAL hard to make too exact a science of it.
Having said all that, I have a spread sheet I made that does basicaly what you have in the link above plus LOADS more...
So take what I say with a grain of salt.
As a learning exersize, projects like what you did are great for reinforcing the way the numbers/volumes interact with each other so you get a much better feel for them in your head.
