It was the external windage and elevation adjustment rings, rather than the optics I was referring to in my reply. Actually, Unertl worked for Fecker before setting out on his own and his rings are essentially identical to Fecker rings. I don't actually know when the design was developed. I was being conservative in saying 60 years. That is the approximate age of my scope.
One advantage of this system is there are fewer moving parts in the scope itself and less to go wrong. Because you move the entire scope for windage and elevation the crosshairs can be fixed and the scope will hold zero as long as the adjustment screws on the rings are holding. If the moving parts on the rings were easily available, it would be easy to fix one of these scopes if it began to wander. They aren't and that is the only issue I have with them.
One advantage of this system is there are fewer moving parts in the scope itself and less to go wrong. Because you move the entire scope for windage and elevation the crosshairs can be fixed and the scope will hold zero as long as the adjustment screws on the rings are holding. If the moving parts on the rings were easily available, it would be easy to fix one of these scopes if it began to wander. They aren't and that is the only issue I have with them.