its fixed g, all the numbers add up to the same shit

No they don't. All the possible outcomes are given the same symbol.

For example:

72, 7+2=9, 72-9=63

19, 1+9=10, 19-10=9

73, 7+3=10, 73-10=63

48, 4+8=12, 48-12=36

10, 1+0=1, 10-1=9

63, 36, and 9 have the same symbol. So no matter how many times you try it, even though the symbol might change, 63, 36, and 9 (amongst the other possibilities) will always have the same one. Even though you can pick any number, due to the formula you can only get a limited amount of numbers.