it kinda works. clever really
spoiler...i am going to look like
if someone proves me wrong
#s 10 - 19 all give you the same total: 9.
#s 20 - 29 all give you the same total: 18
#s 30- 39 all give you the same total: 27
#s 40- 49 all give you the same total: 36
#s 50- 59 all give you the same total: 45
#s 60- 69 all give you the same total: 54
#s 70- 79 all give you the same total: 63
#s 80- 89 all give you the same total: 72
#s 90- 99 all give you the same total: 81
so the only real options it must choose from are 9, 18, 27, 36, 45, 54, 63, 72, 81. it changes the symbols beside each number every time but the symbols for these 8 numbers are always the same. so it always gives you the right answer.
another way to do it is to not bother with the math, just look at the symbol beside any one of these numbers and press the button, the symbol will come up in the crystal ball because it is the only conceivable answer.