All random slot machine games have an underlying probability model. This model is necessary to make sure the game is profitable and to accurately calculate the minimum house edge.

Typical different parts of the games nowadays include the following features: line wins, scatters, holds and nudges, free spins, gambles, bonus games' Some of these features are totally random and the player has no way to influence the outcome. The spin of the reels, for example, is a random event and thus players cannot influence any line or scatter wins. However, in some features (like Hi-Lo gambles and some bonus games) the player has an input in the game. When this is the case, the industry uses the optimal strategy to play the game when building the model. This means that the percentage return advertised for the machine has been calculated assuming the optimal strategy is used all the time while playing the game. Therefore, if a player does not make the optimal decisions when playing the game he would be underachieving, in other words, he would be losing more money than he should lose. For regular punters, understanding the mathematics of the games is vital to have a bit of control.