Around here benchmarks are usually notated with an inverted cone shaped symbol; the point of the cone being at the bench mark with the base of the cone above the location. Typically the bench mark is identified either by number ("BM 1") or name ("BM Bo Didley") and is described by physical characteristic (cut nail in SE side of 24" oak, square cut in top of curb, bonnet bolt at face of fire hydrant, "X" cut in manhole lid, etc.) and elevation. Plans which depict multiple benchmarks often include a table of benchmark dataThe triangle is the universal mapping symbol for any type of randomly located survey control point, which includes all geodetic markers, waypoints, traverse stations, etc. whereas the square is used for points that are not set at random locations, such as boundary corners. In fact, many surveyors refer to random control points as deltas, due to the shape of that letter of the greek alphabet.
I always wondered what those round disks poured into the cement were. They have a date and then another number.Since you want to learn,
and since architects like to be