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The term benchmark, bench mark, or survey benchmark originates from the chiseled horizontal marks that surveyors made in stone structures, into which an angle iron could be placed to form a "bench" for a leveling rod, thus ensuring that a leveling rod could be accurately repositioned in the same place in the future.
B.S is generally taken on the point of known reduced level as on the benchmark or a change point. [1] Benchmark (surveying) – fixed reference point of known elevation with respect to which RL of other points is determined. Benchmarks can be arbitrary or permanent, the former is used for calculation of reduced levels for small survey works and ...
Survey markers, also called survey marks, survey monuments, or geodetic marks, are objects placed to mark key survey points on the Earth's surface. They are used in geodetic and land surveying . A benchmark is a type of survey marker that indicates elevation ( vertical position ).
After careful setup of the level, the height of the crosshairs is determined by either sighting from a known benchmark with known height determined by a previous survey or an arbitrary point with an assumed height is used. Sighting is done with an assistant surveyor who holds a graduated staff vertical at the point under measurement. The ...
The dumpy level was developed by English civil engineer William Gravatt, while surveying the route of a proposed railway line from London to Dover. More compact and hence both more robust and easier to transport, it is commonly believed that dumpy levelling is less accurate than other types of levelling, but such is not the case.
National survey departments of each country determine RLs of significantly important locations or points. These points are called permanent benchmarks and this survey process is known as Great Trigonometrical Surveying (GTS). The permanent benchmarks act as reference points for determining RLs of other locations in a particular country. [4] [5 ...
A benchmark is usually set on the side, marked with the letters "O S B M" (Ordnance Survey Bench Mark) and the reference number of the trig point on a plaque called a "flush plate". Within and below the visible trig point, there are concealed reference marks whose National Grid References are precisely known.
The Abney level is an easy to use, relatively inexpensive, and, when used correctly, an accurate surveying tool. Abney levels typically include scales graduated in measure degrees of arc , percent grade , and in topographic Abney levels, grade in feet per surveyor's chain , and chainage correction.