I’m a little weirded out. I just went to this website: http://www.cyberglass.co.uk/assets/Flash/psychic.swf and it guessed every number that I chose. I noticed that there are repeating symbols, but I still don’t have a clue how this thing works. Any ideas? It must be magic! 
Ah that clever. It took me four goes before I figured it out. I don’t want to give the game away just now - i’ll call back later.
Pretty simple really. Any teens number gives 9, any 20’s gives 18, and 30’s 27, etc. Each of those numbers has the same symbol and each time you try again the symbol changes.
I still don’t get it. I see that the 90’s equal to 81, 80’s equal to 72, and 70’s equal to 63, but how does it know which number I picked? its a different symbol each time. I guess that I’m just dense.
[spoiler]here’s a clue… pick 10 every time.
10 - 1 = 9
or better yet, pick zero
0 - 0 = 0
9 or any multiple of 9 will have the same symbol everytime.
That’s what the whole “add up the digits and subtract from the original number” is, a simple ploy to make sure no matter what number you pick the result is a multiple of 9. It “knows” what number you picked because there is only one result every time. If you don’t believe me then see what symbol you get for a bunch of different numbers before clicking the crystal ball. (They will all be the same symbol)
[/spoiler]
I get it guys! Sorry that it took me so long. I understood the multiple of 9 process, but I didn’t understand that the symbols on the program were actually changing with each guess. Pretty tricky, Thank for your help.