hi john
i made a grid with my computer, then printed it out and took it to a copy store.
they printed it on clear stock ( mylar? ) and i cut it down and put it over my ground glass ( the side that faces you). i did this for both a speed graphic and graphic view II.
i have heard of others using a pencil and ruler and drawing the lines.
pencil and/or mylar works well since they are both reversible ... my drawing ability is poor ( even with a ruler ) so i wouldn't trust anything that i couldn't un-do.