Abstract: A coin-operated entertainment machine has three or four rotatable reels with selectable symbols around their peripheries. The machine is operated by a player, after actuation by insertion of one or more coins, to cause the reels to rotate and come to rest with a combination of symbols displayed on a win line. If the combination is of a predetermined winning nature, an award, such as a payout of coins, is made available to the player. The operating system of the machine assigns an index to each selectable symbol whereby the selected combination can be known before this is displayed to the player. Each winning combination has an assigned rejection probability and any selected winning combination is subjected to an acceptance/rejection procedure using the assigned probability before it is displayed. If it is rejected, a new combination is selected and the procedure is repeated.