For a buck 50 you get those things at walmart....you are probably more familiar with those things with wood beads though....we used them in school, before Al Gore invented the internet! Calculators!
(I am working on a new source for being shunned, I'm afraid!)
I don't shun...
WalMart no doubt sells a fine calculator, but given the rates airlines charge for baggage, the less to be packed, the better.
And, when I say "calculator", what I really mean is an app called V-Planner that designed specifically for calculating decompression stops, ideal gas mixtures, and gas volume requirements for technical diving. It's much faster than running the formulas by hand.