If you don’t want to know how the number finder thing works. From a reader (several got it):
I will admit, and my wife will certify, I’m a geek. This thing bothered me, so I had to figure it out.
If you take any two-digit number, sum its digits together, and subtract the sum from the original number, you always get a multiple of nine. If you look at the chart, all of the multiples of nine have the same symbol. Now it wouldn’t be impressive if the same symbol appeared after each guess; that’s why the symbols change each time you hit the back button.
I hope I haven’t ruined the magic for you.