Bench mark

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  • (anthropology/archaeology) (B.M.): a vertical datum-point usually at a known elevation above sea-level, to which mapped elevations may be related.
  • (geology)
  1. A point of known elevation and position - usually indicated on a map by the letters B. M., with the altitude given (on American maps) to the nearest foot. (Some maps now use meters.)
    Source: Leet, L. Don. 1982. Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
  2. A relatively permanent metal tablet or other mark firmly embedded in a fixed and enduring natural or artificial object, indicating a precisely determined elevation above or below a standard datum (usually sea level); it bears identifying information and is used as a reference in topographic surveys and tidal observations. It is often an embossed and stamped disk of bronze or aluminum alloy, about 3.75 in (9.5 cm) in diameter, with an attached shank about 3 in (7.6 cm) in length, and may be cemented in natural bedrock, in a massive concrete post set flush with the ground, or in the masonry of a substantial building. Abbrev: BM. AGI
  3. A well-defined, permanently fixed point in space, used as a reference from which measurements of any sort (such as of elevation) may be made. AGI
    Source: Dictionary of Mining, Mineral, and Related Terms

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