A "Duh" moment at an estate sale

I was at an estate sale when I came across a container of old pencils, pens, small rulers, and other things. My eye was drawn to a really old protractor.  I hadn't seen one since middle school but it made me think very quickly about what could be done with it.  Topstitching around a corner on a bag or a purse; can be frustrating because your presser foot is turning the corner or making the curve and you can't simply follow the needle plate markings.  By putting an erasable pencil ( make sure you can erase it from your material) in the protractor and setting the distance between the point and the pencil, you can easily guide the point alongside the material and make a mark for topstitching.   Once it's completed you can remove the mark.  Your topstitching will be uniform and straight.  No more wonkiness!