I stuck a sheet of cardboard in my GF and scored this pattern (below), then saved a screenshot of the resulting image before opening the lid. When I need to place something accurately, I can pull up the screenshot to remind me how far and in which direction things are off at a particular place on the bed. (There are more fiddly ways to save a few hundredths of an inch of material, but I’d rather just error on the side of not cutting all the way to the edge than spending the time and energy to figure them out!)
