my earning has decreased!!!

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I just have been member for 3 days... my earning yesterday after update was $0.63 but today when i logged in i found it $0.62... the earning of my first day has decreased by $0.01... other differences would be i got 1 referrals today and i got a alert that i should refer people to this site using my referral link to get a amount equal to 25% of their earning... can any body help why my earning has decreased???