Oh wow, that is really clever. Even with the explanation Jack gave it kind of freaked me out at first like it did Daynar.
The real reason this works so well is that it changes the symbols for the mutiples of nine. Every final number is a multiple of nine, and the symbols for the multiples of nine are all the same each turn, so it can't be wrong no matter what number you pick, unless you subtract incorrectly (Which I did a couple times.
). But the "multiples of nine" symbol changes from turn to turn, so it's not so obvious that it's always a multiple of nine you are getting.
If it didn't change teh symbols you'd catch on when you kept getting the same sybol from turn to turn. And if you tried this trick just using the numbers your subconcious would pick up the pattern pretty quick that the answer is always a multiple of nine. There are so many symbols you have to pay attention to realize they are changing from turn to turn.
Very clever.