I've started to play Astraware's Sudoku (I want to find the perfect Sudoku game for my PPC... hard work

), and there is an option that I can't find what it does. It's that little "N" on the right bottom, that when taped changes into a series of dots, and back to an "N" (you can see it on the attached print-screen).
Does anyone know what's the use of that option?
Thanks!