Crikey, give us half a chance will ya
Personally I like the idea but I can't use it myself because of my eyesight problems. Basically the black, surrounding the pencilmark numbers, next to the white of the grid causes problems with me focussing. Then again, I am partially sighted so that might have something to do with it (which is why I hadn't posted earlier). However, having shown the grid to my father, who is not partially sighted, he felt the same way.
It's difficult to explain the effect - another reason I didn't post earlier - it's like: sometimes houndstooth check on the TV makes your eyes squint, which is why nobody on TV wears it.
If you could find a way of reducing this effect (and making the big number squares bigger, so that I can make the big numbers out a lot easier too) I'd be able to use it, but I do think that it's a good idea.
Luna