I was dismayed to find the batteries had corroded and ruined my trusty HP-41C, which I bought back in '82. I loved that calculator. I programmed my first hack on it. You could set a flag to run the first program in memory on startup. If someone walked away from their desk, I would grab their HP, write a program to turn the calculator off, then set the flag. It was fun prank, and it actually got a few people interested in learning how to program theirs.