Wehrmacht K98 aim corrector (Zielkontrollapparat). The aim corrector was mounted to the rear sight and is used for instruction during dry fire excercises. The cadet looks thru the glass and aligns the sights on the target. The instructor observes from the side to see the sight picture reflected in the glass and can coach or confirm the correct sight picture. The aim corrector was mainly used for training with the K98 rifle and its .22 variants. The aim corrector is nicely 'D.R.G.M.' marked. Rare original example in very good condition!