1. With right sides together, place a purple or green print C piece atop an arc unit; align marked dots and pin at center (Diagram 8). Pin pieces together at each end, then smooth C piece along arc until edges are aligned; pin approximately every 1", picking up only a few threads at a time (Diagram 9). Sew pieces together, removing each pin just before needle reaches it. Press seam toward C piece.
2. Aligning marked center dots, pin Step 1 arc unit to a purple or green print D piece (Diagram 10). Pin edges and stitch as in Step 1 to make a block (Diagram 11). Press seam toward D piece. The block should be 12-1/2" square including seam allowances.
3. Repeat steps 1 and 2 to make four blocks total.
4. If temporary foundation material was used, remove foundation with tweezers or the blunt edge of a seam ripper.