Even if you don't own a reliable square, you can still check for square by measuring between opposite corners on a project. If the diagonals measure the same—and the opposing sides are equal length—you know it's square. If clamps interfere with this measurement, or you're gluing up several identical assemblies, try this simple alternative. Cut two scrap strips, each a few inches longer than half the length of the diagonals. Then cut one tip of each strip to about a 30° angle. Hold the strips together with the angled ends in opposite corners and clamp them together. Using this as your gauge, measure the other diagonal to confirm a square glue-up. To equalize the distances, lightly clamp across the diagonal corners that are farther apart.—from the WOOD shop