Excuse me, what is the principle of that digital mind reading?

The principle of digital mind reading;

Let ten digits of a two-digit number be A and one digit be B, then this two-digit number is (10a+b). The sum of ten digits and one digit is (a+b). Then according to the specified method, the result is (10a+b)-(a+b)=9a.

Obviously, no matter which two-digit number you choose, after this operation, the result is always a multiple of 9, which are 9, 18, 27, 36, 45, 54, 63, 72, 8 1 respectively. The result is always 1 of these 9 numbers. This is the whole secret of this game.

The next step is simple. The designer of the game designs all patterns of numbers corresponding to multiples of 9 to be the same. So, no matter what result you get (which of the nine numbers), it will have the same pattern. Just make the pattern in the crystal ball consistent with this pattern. Because every time you click on the crystal ball, the pattern will change, so you can't find the secret at once.