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"...recovered but not occupied..."?

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What kind of instruments did they use. I read an "occupied" log from the 50s. Something about hanging a light or something? I can't remember exaclty, or what BM it was, but how were BMs in say, the mountains of the Sierra located, placed, and occupied in the 40's and 50s?


Occupied usually means they set up an instrument on the point to make measurements.

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Briefly, the marks were set either as horizontal control marks or elevation control marks. In the profession, the latter are the only ones correctly denoted by the term "bench mark."


Bench marks were set during leveling runs, in which crews working with vertical measuring rods and leveling telescopes measured heights, starting at known points. Horizontal control, until GPS came along, was done by triangulation--trigonometric measurement of triangles, using a theodolite, with marks set at the corners, starting from baselines measured with extraordinary precision.


Triangulation involved sighting over much greater distances than are typical with leveling, so the effects of atmospheric and meteorological distortions could be minimized by working at night. Crews included light keepers, who went to specified points and turned on their lamps at appointed times.


The lamps and the instruments were usually mounted on tripods, centered with great care above the points, and their height above the points measured and recorded. "Height of light above station was 1.66 meters."


This is very cursory. Much more detail is available in downloadable NGS publications put out over the past hundred years. See http://docs.lib.noaa.gov/rescue/cgs_specpu...s_specpubs.html.

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In the profession, Occupied means a person physically set up a survey instrument on the point and made measurements from it to other points. Its is also a term used by a horizontal survey team (e.g. Triangulation, Traverse, GPS). A leveling crew would not use the term, the would say "not leveled to".


It could mean several things but without more knowledge who knows what the person writing this meant.


It could mean they looked for it, found it but never used in for their work at that time.


It could also mean they never set up a survey instrument on the point, only sighted it from another point.

Edited by Z15
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