I work at an independent family center (the local Chuck E Cheese is one of our primary competitors) that has no less than eight cranes, though they're all substantially newer and cheaper than the one you were playing.

I think that box is part of some kind of retrofit kit (upgrade kits and conversions are HUGE in the coin-op world) to make an old hard-to-calibrate crane into a "smart" crane that dynamically adjusts the claw voltage (and thus, strength) on the fly. It's the "skill still required" kind of rigged -- the better you are, the more likely you are to win, but the machine adjusts itself to ensure a certain payout averaged over a certain (large) number of plays. Specifically, each time someone wins it gets much harder, each time someone loses it gets slightly easier. So, skill is still very much so involved, but luck (specifically, how well those that went before you did) is a larger factor.

"Set perc" is most likely the operator setting of how often he WANTS the crane to pay out (that is, how often a prize is won), and "Current perc" is how often it's ACTUALLY paying out. So, it's currently running on the easy side of its scale in an attempt to bring the payout up.

I should note that cranes this smart aren't typical. Most cranes are the dumb "three voltage / interval" types where they simply up the claw voltage every X plays regardless of whether that play is a win. I wish we had the smart ones -- prize cost would be a hell of a lot easier to manage, and we could be more honest with our guests.