AK-47 Aim Training Correction Device, ZGK-71 (Zielübungen Gerät Korrektur). SHOW AND TELL 157

SHOW AND TELL [157]: ZGK-71 (Zielübungen Gerät Korrektur = Target Practice Device Correction) or Aim Training Correction Device. East German, possible usage on AK-47 and/or Mosin Nagant type of platforms.
(Update, the paddle with multiple sized apertures may possibly be used for range estimation of known sized targets)

Wikipedia article on Collimator sight : https://en.wikipedia.org/wiki/Collimator_sight

Wikipedia article on Collimator : https://en.wikipedia.org/wiki/Collimator