I know this idea is out there but here goes. If you have a piece of clear plastic acrylic rod about 1/4 inch in diameter, you can make a homemade spotting scope with it. Cut the rod to a short length, about 3 to 6 inches, polish one end flat and the other end convex. Then take a scribe and scratch two crossed lines on the convex end. Next rub a black colored magic marker on the convex end and polish it. This should leave the black only in the scribed lines. When you look into the flat end you will now have a very accurate spotting scope. Since the rod is plastic it can be heated and bent to a convient viewing angle. Fixture it in your mill and line use the procedure I described with the fine point. This should give you a very accurate measurement.