Probability dont match up

The idea is great, but the problem is that if you put the same two cards one time then repeate it again the numbers will different. How can you trust a calculator that gives different results if you enter the same equation? The results change up to 0.5% which doesnt seem, but when you see it change, you stop to think if the equations done here are really accurate.

edsauer about Poker Odds Calculator, v5.1