Tight Slots (slots)

Tight slots will have worse payoffs to a "certified" high of under 100%, on average over a period time. A machine not having a symbol, let's say 2-3 cherries, which pay a couple of coins. These cherries would replace a symbol that doesn't pay, and presto you have a tight machine. The less paying symbols a machine has, the smaller the probability of payouts - thus a tight slot.