Abstract: The invention provides a foolproof way for distinguishing between occasions when beam imbalance is caused by manufacturing inaccuracies and when beam imbalance is caused by presence of a counterfeit coin among the coins being weighed in any one of the three weighings needed for a demonstration of the classical solution of the well-known twelve coins weighing problem using equipment of modest cost. According to the invention, the demonstration equipment is modified so as to include a compensator element which when placed at an indicated location upon the high side of the balance beam in any one of the three weighings which cause noticeable swinging of the balance beam only if there are only genuine coins being weighed in the respective weighing.