Contributing expert John Robison writes:
Random does not mean completely unpredictable. Consider, for example, drawing from a deck of cards. We know we can draw a king of hearts. We also know we can never draw a jack of livers or a queen of spleens, because those cards aren't in the deck.
Okay, that's silly, but here's my point: What’s random about drawing from a deck of cards is which available card you’ll draw next. Despite this randomness, we do know all sorts of things about the cards you might draw. We know that one-quarter of the time, you'll draw a club, one-quarter of the time a diamond, one-quarter a spade, one-quarter a heart, and never a liver or spleen. We also know that one-thirteenth of the time, you'll draw an ace, one-thirteenth of the time a deuce, and so on. We know these things, because we know the population in the deck of cards from which you’re drawing.
A slot machine works in exactly the same way. There's a population of possible outcomes and the Random Number Generator is used to select one of those outcomes as the result of a spin. We don't know what result will appear next, but we (well, the manufacturer and the casino) know how many times each combination appears in the total population and, therefore, how likely it is for any combination to land on the payline. With that information and the paytable, we can calculate the long-term payback for the machine.
Note that I said "long-term." Over the short-term, anything can happen. But as the machine gets more and more play, its actual payback will get closer and closer to its long-term payback.
Number of spins, incidentally, is how time is measured on a slot machine. Given the number of spins, we can calculate the range in which the actual payback on a machine should fall with a given degree of certainty. The actual payback on most machines is within a percentage point of the machine's long-term payback after a million or so spins.
So the answer to your question is, a casino can honestly and accurately claim that a slot will pay back 99%, but no one knows where the returns will show up to make up that percentage.
John is author of The Slot Expert’s Guide to Playing Slots, an invaluable, pocket-sized guide for all slot enthusiasts.
