hm.. ok - when you are working on BOTH the interior and external
   angles of a polygon at the same time, you end up with 4 angles -
   like a cross shape but not 90 degrees each but rather than
   angles produced by the 1st vertex of the polygon. - like < if it
   is an angle, could be extended *past* the point and across to
   the other side... to form a " X " shape - a grid.with four
   angles to measure."