Anyone know how this thing is supposed to work, it's approximate age, and any other pertinent info about it? Friend of mine picked it up at some flea market/garage sale and has asked me about it. It has "Mod 80 Johnson" inscribed on it. I can't figure out where the line is even supposed to come out of it with the hole in the center of the plate and then another two holes at the edge of that same plate 180*, or directly opposite, one another.





Showing one of the "edge" holes - purpose of these?