They mean it when they say "those things hidden from the player are almost as fascinating as the things visible. The motors, gears, electrical wiring, and gadgets have an appeal all their own."
Indeed, they offer an extensive section called Mechanisms Explained in which they have documented, photographed, animated, and described how a wide range of arcade machine mechanisms work. They offer mechanism explanations for the following:
• Ball bearing baseball "runners"The Sands Mechanical Museum is an extremely well documented online mechanical reference source.
• Bingo display screen (mechanical)
• Various coin payout devices
• Coin counter units
• Coin rejector workings
• Coin slide mechanisms
• Credit recording unit
• Gear box based hunting game
• Photo booth camera with Geneva mechanism
• An early score keeping unit