GERMAN OPTIC SCOPE

This one has stumped so far, I have tried the online sites but have not found out the proper nomenclature or use for this. It's like a misty it has the late war tan paint, it had a flip down cover for the front lense (broken off) like a navy item. The only marking are for the internal sun shields. The lense has almarked line from center marked 100 going left down to 50. The right line goes from 0 to 50. I have not seen any other scope marked this way there is a complete leveling bubble on the base. It reminds me of the instrument we use to line up the artillery when we would first set up. Condition PK lense are clear.