horizontal line
line parallel to the mean spheriodal surface of earth
line passing through the center of cross hairs and the center of eye piece
line passing through the objective lens and the eye-piece of a dumpy or tilting level
foresight only
backsight only
foresight and backsight
foresight and intermediate sight
backsight
intermediate sight
foresight
all of these
99.345 m
100.345 m
100.655m
101.870m
concave
convex
plano-convex
plano-concave