Looks like the site is down for me... Launch is going less than perfect.
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And what jackpot? Now I'm curious.
As I understand it, if you roll exactly 77.77 on any bet, you get 10 times your stake as a bonus. Your bet is settled as usual, and whether you win or lose you still get 10x your stake back.
There's a 0.01% chance of hitting 77.77 - that's 1 in 10,000 - and it returns 10x stake, so it effectively takes 0.01% * 10 = 0.1% off the house edge, leaving the house edge at 0.90%.
Edit: also, from what I've read, there's no limit on this, other than the regular limits. So if you bet the maximum bet of 39.5959 BTC at 98% and hit 77.77, you get a jackpot payout of 395.959 BTC - that's worth around a quarter of a million dollars.
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I hope they are ready for that possibility... because like death, the law of large numbers is inevitable.
Suggestion: An improvement on the jackpot is to make 7.77 and 77.77 payout 5x each, conserving that 0.9% edge yet giving people more incentive to roll... multiple smaller rewards with higher probability is psychologically more incentivized than a big reward with lower probability to the player IMO.
EDIT: Removed the % sign... brainfart.