In that crystal ball thing...there are only like 5 different symbols, and they rotate through the number that corresponds to them. If the symbol for 0 is say the circle with a star in it, the next time you click, it will correspond to lowercase psi, etc. Most people wouldn't notice since they are looking at different numbers and corresponding symbols every time. Doing this gives the illusion that there are many many options and it's "reading your mind" or something. Now, since we've established that only 4 or so symbols pop up, lets look at number you can choose:
10: 0 + 1 = 1 10 - 1 = 9
11: 1 + 1 = 2 11 - 2 = 9
12: 1 + 2 = 3 12 - 3 = 9
13: 1 + 3 = 4 13 - 4 = 9
Gawd I'm a genius.
jk it took me like 3 mins to figure that out