TO test if I had my norton flat, I drew a grid with a number two pencil. Not waterproof, and lapped until it was gone. Is there any other way to tell if I have it flat enough? I seem to be getting some resistance on the 4k side and I am not sure if I have it flat enough. I lapped it quite alot with a flattening stone and the pencil grid, (the best I could do free hand) was gone in a minute or so. Is it lapped sufficiently?