The crystal ball will read your mind, try to guess how it works :).

http://wwwimage.cbs.com/primetime/ghost_whisperer/swf/crystal_ball.swf

 

 

 

 

Try it first then scroll down to find out how it works!

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When adding the digits of of a two digits number then subtract the total from this number,
the output will always be 9,18,27,36,45,54,...or 81.

So for these numbers, the symbol is the same and later it will appear in the crystal ball :)