Magic Screen as found in Bingo (pinball) Machines
(mouse over the buttons to see the steps or "PLAY" to see the animation)
This device rotates a screen in front of a bingo card full of numbers. Three balls in a row, in either red, green or yellow, will pay specified odds. By gambling more money, the player is able to shift the screen to other colors and hopefully increasing the payout. (See Phil Hooper's amazing Bingo Pinball Web Site for more information.)
The motor in the lower right of the picture, works through a leather clutch to rotate a notched wheel in the bottom track of the magic screen. Each screen has a peg on the bottom that engages this notched wheel, causes the screens to rotate.
The motor also rotates the chain through an idler gear to a large wheel in the center bottom of the picture. This wheel rotates a large wheel with electrical fingers and contacts, informing the game what the current position of the screen is. This information is used to determine winning positions.