Can someone expplain how this works?

OK, so I went ot this cute little site here.

Basically, you choose a two-digit number, add the two digits together, then subtract that number from your original two digit number. For example, you choose 54, 5 + 4 = 9. 54 - 9= 45. Now, each number from 0 to 99 has a symbol associated with it, after finding the right symbol for the new number, you click on the crystal ball, and it, with amazing accuracy, shows your symbol.

It didn’t get the right symbol for me the first few times I treid it, but after that it has worked every time. I noticed that some numbers share the same symbol, and the the symbol assiciated with each number changes after every try, but I still don’t see how just those two things can make it that accurate. I’m very bafled :confused:

Oh ,nevermind, I see how it woks now. Basically, no matter what number you choose, only a certain set of results can exist, and all those results have the symbol that shows up.

Also being discussed here:

dammit…Mods, please close.