Qualifying
Usually only players who wager the maximum number of credits per play qualify to win the jackpot. All wagers, whether or not they are maximum credit bets, contribute to the jackpot though. As a result, a game which requires a 10 credit wager to qualify for the progressive jackpot will tend to have the progressive jackpot rise to higher levels (relative to its break-even level) than a game that requires only a 5 credit wager to qualify.
Read more about this topic: Progressive Jackpot