Step 3   Once you have made your mark, take a square, such as the speed square you see here, and extend your mark across the width of the board. This is important as it makes lining up your mark on the radial arm saw, Miter saw, or with the hand-held circular saw much more precise. Again, make a noticeable mark, but also note how the width of the line affects where to cut. Ideally, you should be able to set the saw to just trim off the mark and achieve the exact length you are looking for.