Pair up a dark and a light square right sides together and all edges aligned.  On the back side of the top square lightly mark the diagonal. Next, carefully sew  a scant 1/4" away from the marked diagonal on each side of it. After you have done this cut apart on the solid lines, between your stitching.. Each square pair will give you two half squares. Press them to the darker side, and trim to measure 3-1/2" if needed. You need a total of sixteen half squares...