Woodworking Tip #2: Corner Cut Outs

The corner cut outs in the floor and ceiling of the recently posted Illuminated Display/Trophy Case had to be identical and precise.  This was achieved by vertically clamping the piece to the back of a single-slot sled, moving away from the fence with a spacer block (to clear the waste piece), and passing through the blade, which was set at the required height.  Thus both the height and the width of the cut out were accomplished simultaneously.  The photo does, however, have a minor error.  What is it?