Re: Users and printing devices...
WAAAAAY back in the day, the Engineering department at university had one of those desk size flatbed Xerox (yes, it was that brand) machines with a slot for the "counter key"...an odometer-like device with six pins that needed to be inserted before the machine would make copies. Annoying, you had to go, cap in hand, to the department secretary and ask for the key. Depending on her mood, you might or might not get it.
I was browsing one of the electronics magazines (yes, this was a while ago) and noticed that one of the surplus places had the key counters for sale at a very reasonable price. So I ordered a couple.
A week or two later, I waited until no one was around, and tried the keys I'd bought in the machine. Sad trombone...neither worked. So, I went up to the lab, procured a multimeter, and measured the resistance between the six pins. Sure enough, a couple of them were shorted together. Then, I went and borrowed the official key, and measured its six pins. Different pair shorted. Returned the genuine key, after making a note of which pins were connected, then proceeded to dig the epoxy out of the screws in the case of one of my purchased keys. A bit of fiddling with the soldering iron and I had what I hoped was a duplicate key...which worked just fine when I tested it in the machine!
Of course, the statute of limitations (as well as counter keys) has long since expired. And I never misused my bounty...but it sure was a timesaver when I needed a quick copy.