How casinos are layed out, from the positioning of the tables, down to the lighting and carpet patterns, is no accident.  But nothing is more directly related to end-of-the day profits than the strategy of the carefully placed slot machine. With slot revenue now accounting for 85% of profits, the slot machines of today are continuous and uninterrupted, allowing for minimal effort on the players part resulting in maximum financial loss.

2014 Slot-machine science How casinos get you to spend more money