Slots are the casino industry’s most powerful revenue generator. Whether you’re playing a simple three-reel stepper or the latest incarnation of a video game with bonus features, you’re wagering on a mathematical model that determines your chances of winning and losing. This mathematical model, coupled with the design and behavioral psychology of the game, makes slot machines powerful influencers on gaming floors.

When you play a slots machine, you place either cash or, in “ticket-in, ticket-out” machines, a paper ticket with a barcode into a designated slot. You then activate the machine by pushing a lever or button (either physical or on a touchscreen). The reels then spin and stop to rearrange symbols, which may include traditional icons like fruit or bells or more elaborate images based on the theme of the machine. If the symbols align with a pay line—a line in the center of the screen that shows all winning combinations—you earn credits based on the machine’s paytable.

Today, the slot machine is more complex than ever, but its basic structure remains the same. The machine takes your money and pays out a percentage of wins—which is determined by a random number generator—based on its pay table. The visible reels simply act as a courtesy to you, displaying the stops that the RNG has already selected. While other games require you to have some gambling knowledge or skill, slots are purely a game of chance. That’s why they’re so popular.