Buy the one that has a slot in the middle and edges that are 1/4" on either side. I use it for 1/2" sq triangles. You put point on each corner diaginally and draw lines on both edges and then sew on these lines and cut down center. This gives you 1/2 sq triangles. It is not really very time consuming to draw 2 lines (not three) and makes triangles easy. Actually this ruler is not very expensive and is well worth the cost even if it not used often. Anything to make you life easier.