i bleive this challange may have been posted before, never the less here goes.

you have 3 wieghing scales, a normal scale that gives the correct result, a reverse scale that gives the oppisite result, and a random scale that gives, well you guessed it, a random result.

you have 4 normal coins and 4 heavy coins. your task however is to simply identify which scale is which with the fewest weighings, and you don't intially know which coins are which either.