RNG machines had a limited number of settings, and someone had to instruct the workers on what setting to use each time. However, true randomness was impossible to achieve. Casinos used to hire a separate workforce to install and adjust the RNGs that kept their slot machines random. The machines’ randomness was achieved through an invention called a random number generator (RNG). These reels would spin for a while thanks to kinetic energy and then come to a random stop.īecause the system was entirely mechanical, the winning odds of these games had to be set mechanically, too. The reels were attached to a physical lever the player was supposed to pull to set them in motion. Original slots were standalone machines with three mechanical reels, each bearing ten symbols. The slots we know and love evolved from an older, well-known game.