GSR Geo Double Prism Optical SquareThe Geo Double Prism Optical Square comprises two pentaprisms of quality optical glass, housed in a sturdy aluminium casing. The housing cover can be rotated to cover the viewing window and protect the prisms when not in use. The prisms are mounted above and below the through sighting window, the upper one sighting from the right side, the lower one from the left. The pentaprisms are ground to refract the views by exactly 90. Easy to use, simply hold