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Player with unluckiest losing streak: Samsung Galaxy Tab 4
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Just to make it clear, is it dependent in any way on % chance/payout rate/amount wagered, or is it irrelevant?

Yeah it's based on chance, the probability of losing x bets at y chance. Whatever the least likely run is (unluckiest) wins.

OK. But the amount wagered doesn't matter?

And I assume the mixed streaks (losing bets with different chances) won't count?

Stakes don't matter and all losses have to be in a row at the same chance yeah.

can we see the stats who has done the most somewhere?

I'll get a leaderboard up asap. In mean time you can click a user name in chat or on all bets tab to see their stats.