Mason Range finder sight. You would measure how high you were in a tree, unlock the brass knob, slide the setting indicator to the height you were, then the tighten the knob back down. Then, an animal would walk in, you would turn the sight on by pushing the black button you see at the end of the wire in pics, and then, the pins would light up on what distance you were aiming at. If 2 pins lit up, the animal was the yardage between your set pins. It was basically a lighted pendulum sight. $80 25 years ago. Lol. It actually worked quite well. Runs on a 9 volt battery. This was invented before fiber optic light gathering sights were even on the market if I remember right. I saw a guy in bear camp in the mid 80's in Canada use one on his bow successfully on a 400# bear. He talked it up and I had to have one. I killed a lot of deer with it on my bow Bear Whitetail II and Bear Alaskan II.