If the groups are in equilibroum, then
 The false coin is one of 3 coins interchanged at step (A).
 The false coin is lighter then the good coins.
 If the plates switch positions, then
 The false coin is one of the coins interchanged at step (B).
 It is not known if the false coin is heavier or lighter then the good coin.

If the plates are in the previous position, then
 the false coin is among the remaining three heavy coins
 The false coin is heavier then the good coins.
