Remove the 3-inch piece and measure up 2-inches from the top; make a light line or mark. See Figure E.

At the mark made from the intersection of the 3-inch and 4-inch measure over 1-inch. See Figure F.

Draw a line connecting the two marks extending it past the intersection mark. From the intersecting mark, draw a 45-degree line down, away from the 4-inch piece, until it connects with the lines just drawn. See Figure G.

Carefully cut along the line removing the section just drawn. This piece will be the one that slides along the 4-inch measure, the cut out area allowing for easier reading. See Figure H.