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Our little stay-cation comes to an end as we ready to welcome Colleen and Shane this afternoon for their Full Cave class.

Nelly is putting the finishing touches on their cottage while I'm burning through a modest-sized forest-worth of printed paperwork for them. And then... it's on to lamination.

I love my little laminator. Most especially for the form HERE.

This form is to quickly and graphically figure out how to gas match your thirds among a team wearing dissimilarly-sized tanks.

Nearly everyone in this area uses AL80, so gas matching is streamlined. But pretty nearly everyone I think I've worked with either has dived or plans to dive (and should dive) in Florida, too.

In Florida, though, every day is anything-can-happen day as far as what your buddy is going to show up wearing. And what sometimes seems like common sense (something like, "give the heavier breather the biggest tanks") counterintuitively presents its own, new problems... like needing to do math.

Thing is: I hate math. Because I'm terrible at it. I get really resentful when people who are good with math pull that, "It's really easy, actually," shit.

There are plenty of times when I've got someone that need such a table, for whom numbers are the music of the universe. I always imagine they see the world like Neo when he rises from the dead.

But me? I'm 47 years old and still do arithmetic on my fingers; you want me to do algebra of vital importance in my head? I do that = we're all gonna die.

So, for the rest of us, I give a laminated copy of this chart to all my students. Trimmed just so, it fits right into the back, windowed pocket of a wetnotes.

Obviously the first column is Tank Size. The numbers along the first row are Usable Pressures. All the numbers in the middle matrix are Useable Volumes. Find the useable pressure of the limiting diver on the team, trace your finger down to their tank size for useable volume. Now find that volume for everyone else's tanks on the team and trace up for their useable pressures. No math required, Excel did it all.

There is a long-hand version which, of course, we review in class. Every cave diver should understand what these numbers are and what they mean. And anyone diving dissimilar tanks should be doing this at the start of every single dive.

That doesn't mean you should have to endure a struggle with them every single time like Jacob wrestling the angel.

Another option: you could just all dive the same sized tanks. That doesn't even call for a chart.

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