Quoted from Oldgoat:
By the way, is there some chart or easy formula to determine if the impedance on a coil is correct? I've always just measured two of the same type, but if you only had one of a particular type in a game, how would you know what the correct reading should be? Of course, based on my first statement, this may be moot since it seems like the only test needed is 1) Does the coil fire
As long as it isn't 0 ohms, you can just compare with an identically wound coil to get an idea of what it should be. Two identical coils will probably vary slightly as well in ohms. Nothing wrong with that.
As for a table or chart, I'm not sure that is really even necessary. You can always A/B reference coils in a pin. More windings = higher ohms = more resistance = lower power.
In a case where the wrapper fell off, and you're not sure what you're looking at, you can clip the diode on one end, read ohms, and compare it to another similar coil to make sure it isn't much lower or higher power, but you'd probably know it is weird just by the gameplay. You would want to clean up slop first (tight coil stop, clean plunger and new sleeve) before assuming anything though. There is really no rule for the strength of coil you use in a particular location either, except for overly powered stuff that could cause things to break on the game.
For instance, the upper flipper in my Sorcerer I think is way overpowered for what it needs to do. I dropped it down in power to a higher winding coil to prevent damage.