Can somebody explain to me what an optical square is and why it is used in land surveying?

Can somebody explain to me what an optical square is and why it is used in land surveying?

Can somebody explain to me what an optical square is and why it is used in land surveying?
Optical Square is an old term, (I have not heard that in years) for a Right-angle-prism.





It is a small device which, when looked 'into' allows you to see lines to the left and right which are at 90 degrees to your line of sight.





It will allow you to roughly (emphasis on the word rough) lay out a grid pattern (as in cross sections), station and offset points, or approximate large square areas such as a football field.





Primarily it is used for grading work where precision is not as critical.





Personally, the old clap your hands works just about as good.
Reply:It is actually called a "right angle prism". It is used to locate objects by station and offset from a baseline.