I have actually never seen this before but its pretty neat.
If you pick any number from 90-99, you will always land on 81.
If you pick any number from 80-89, you will always land on 72.
If you pick any number from 70-79, you will always land on 63.
etc.....you always land on a number that is a multiple of 9. 81,72,63,54,45,36,27,18, or 9.
Each time you refresh, the symbols change, but these set of multiples of 9 will all have the same symbol.