Interesting indeed. The two photo's at the links show the protractor in one but not the other. I wonder how the protractor is measuring elevation since it's stuck to the side at the top with gum. Something simple that points to "down" seems to missing in the images. That something would cross the protractor and yield elevation.

How could this be improved with a modern glass/plexiglass signal mirror with a fireball. I may need to breakout my mirror and a protractor, and play around.