Lady Esmeralda's Crystal Ball is based on simple deception.
You THINK you can pick any number between 1 and 100, but in reality the mathematical equasion you are asked to calculate in your head allows only a handful of results:
0, 9, 18, 27, 36, 38, 45, 46, 52, 54, 63, 67, 72, 77, 81 or 89.
No matter which number betwen 1 and 100 you start out with, after subtracting the 2 digits from the original number, you always end up with one of the numbers listed above.
And if you look really close at that chart of symbols, you will notice that everyone of the possible answers has the same symbol next to it.
So why do you get a different symbol every time you try the trick again? Because the chart changes every time you try it again. Every time you start over, the symbol next to all possible answers changes into a different symbol. For example, look at the symbol next to 0 and 81 right now. Then start the trick over and check the symbol next to zero again... It changed!