I'm a geek. I know it, and now you know it. I'm not ashamed.
Now that's out of the way, let me introduce my latest gadget, the Under $50 O2 cell Checker. In fact, I estimate my costs were closer to $35 -$40.
I put a lot of pics and a detailed description on my website - follow this
LINK to see it for yourself.
The short version - using a variety of bits from my rebreather, things I had laying around, and some common hardware store items, I was able to create a fully functional, 3-cell, Cell checker for well under the cost of a single cell.
I hope you enjoy.