Bench mark

Bench Mark - A relatively permanent point whose elevation above or below an adopted datum is known.

These Bench Marks have a measured height above MSL/AHD, but generally no known Latitude and Longitude. They are usually found along the side of roads, where optical levelling is easiest.

Temporary bench mark; Tunnel boring machine
TBPLS
Texas Board of Professional Land Surveying ...

In the case of height datums, it suffices to choose one datum point: the reference bench mark, typically a tide gauge at the shore.

VABM: Vertical Angle (elevation) Bench Mark
VGA: Video Graphics Array
VI: Vegetation Index ...

See also: Information, Mapping, Location, Survey, Area