I used a piece of notebook paper and made a heavy crease fold (90 degree) and l put half behind the frame and half on top with the crease snug on the corner. I then felt for, and rubbed through the paper the holes on the backside of the frame. I marked with a pencil the top edge of the paper. I then refolded the paper, so the dimples rubbed in the back now draped over the front, lining the top edge up with the pencil mark and the fold snug with the top front frame corner. Drilled the center of the dimples = perfect alignment.