Hi Milton,
Just use some electrical tape to hold the sandpaper down on the glass and rub until flat. To be sure you have it thoroughly flattened, draw a light figure eight on the surface of the Norton and then take a couple of passes on the sandpaper. If it's flat the 8 will disappear evenly. Then most guys will round off any pointed corners on the surface of the stone. Others may add some other points to this post, as I am not the Honemeister Deluxe. Good luck!