The only reason I could see for grid lines is to get the workpiece parallel to the X and Y axis. I found a much easier way to do it. My spoilboard is deeper than I could flatten with the bit. This left a perfectly parallel lip on the front. I have a couple of pieces of MDF that I ripped on my table saw that I push tight to that lip and then the workpiece tight to the MDF. I then secure the workpiece. The 1F is way more accurate than my eyes to be looking at lines.