If I am trying to draw a rectangle or square on a piece of paper I can use existing corners of the paper as a start point. However I lose accuracy when completing the square or shape on the inside of the paper. In some cases I plan on cutting this and using it a template. I measure corner to corner to verify accuracy and I usually have to settle for good enough. If I had a square (ruler) I don't think I would be having an issue or at least not be adjusting my lines as often. Using just a plain ruler and pencil is it possible to draw a perfect or near perfect square or rectangle? i.e. set of 4 right angles.