The Return-to-Player Number on a Slot Machine
The figure published for a slot machine is a return to player, which is the complement of the house percentage. A machine described as returning ninety-four per cent has a house percentage of six.
The number is a property of the machine's own table of outcomes, computed over the whole cycle of possible results rather than measured on a floor. It is exact in the same way that the roulette figure is exact, and it is just as silent about any particular session.
Two features of modern machines make the figure harder to read than it looks. The first is that outcomes are drawn continuously by a random number generator and mapped onto the reels, so the visible symbols are a presentation layer rather than the mechanism. The second is that the same machine model is frequently manufactured in several configurations with different returns, and the one installed is chosen by the operator.
So the published return describes a configuration, not a cabinet, and never a particular spin. That is the whole of what the number claims.