That is the money deposited by the player in the machines. When casinos look at how a slot machine is performing, the most basic number they look at is the drop. “It is all,” he says, “about the game math.” To explain why they are so reliable for casinos, I talked to Bob Ambrose, who broke into the industry at the Tropicana Atlantic City in the early 1980s and is today a gaming consultant and casino management instructor at Fairleigh Dickinson University. Slot machines appeal to casinos because they are, as long as enough people play them, stable money-makers.