Instead of having a ruler or a protractor one might simply have the ability to reference past lines. with the use of a reference tool, one could establish relationships relevant in the file. It might tell you what angle two lines form and set up a scale internal to the document. I mainly use Goodnotes to draw geometry because of its wonderful shape tool. It is much easier to use rather than constraining to the grid which feels awful, much like other programs. The drawback in goodnotes is there is no sense of scale or relationships.