Most games however still require the symbols appearing left to right, sometimes this even includes scatters. Each slot machine in the group contributes a small amount to this progressive jackpot, awarded to a player who gets, for example, a royalflush on a video poker machine or a specific combination of symbols on a regular or nine-line slot machine. In some games, wild symbols can appear only on certain reels. The reels are spun each play, and if certain combinations of symbols appear then winnings are paid by the machine, or a subgame is played. The two Iowa cases of State. Combinatorial analysis and/or computer simulation is necessary to complete the task. On both systems, scatter symbols still pay in the darkened areas just like standard machines where scatters don't have to appear on a payline. A person playing a slot machine can insert cash, or in ticket-in, ticket-out machines, a paper ticket with a barcode, into a designated slot on the machine. The drums themselves were driven by stepper motors, controlled by the processor and with proximity sensors monitoring the position of the drums. However, this is not mandatory and can be changed from game to game.