Marking the halfway point of the sheet

The first task is to get these sheets cut in half, making two 48" x 48" squares from each sheet. I needed to be sure to find the center line fairly precisely or I'd end up spoiling one of the squares making it under 48" while the other was over 48". So out come the extra fancy tools of a tape measure and a Sharpe. I marked a few points at 48 inches then looked around for a straight edge. A piece of scrap wood was handy so I used that for drawing a full line down the middle to guide my cut.