Benchmark (surveying)

This article is about the use of bench marks in surveying, for other uses see Bench mark A bench mark in every-day language is a point of reference for a measurement. In surveying a bench mark is specifically any permanent marker placed by a surveyor with a precisely known vertical elevation (but not necessarily a precisely known horizontal location). These reference points may be chiseled into a wall, or more typically, marked by small brass or aluminium disks, iron pins or bolts that are permanently attached to a stable foundation, such as concrete posts, bridge abutments, buildings, or a specifically constructed concrete block. These markers are then used as starting (control) points by subsequent surveyors and other users to establish the elevation of nearby points.
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