I've seen that before and was baffled by it. Then I decided to try to figure it out and I think I did.

It works cause any number you choose, when you add them together and subtract from the original, you'll always get the same number within the 10 digit range

62 = 54
63 = 54
64 = 54
88 = 72
87 = 72
86 = 72

54 and 72 will have the same symbol...