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The top mark is at 1,500 mm and the lower is at 1,345 mm; the distance between those two marks is 155 mm, yielding a distance to the rod of 15.5 m. Optical levelling, also known as spirit levelling and differential levelling, employs an optical level, which consists of a precision telescope with crosshairs and stadia marks.
An Ordnance Survey cut mark in the UK Occasionally a non-vertical face, and a slightly different mark, was used. 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 ...
The commonly used datum is mean sea level. [3] Dumpy level – optical instrument used to establish or check points in the same horizontal plane. It is used in surveying and building with a vertical staff to measure height differences and to transfer, measure and set heights. Also called a builder's level or leveling instrument.
A level staff, also called levelling rod, is a graduated wooden or aluminium rod, used with a levelling instrument to determine the difference in height between points or heights of points above a vertical datum. When used for stadiametric rangefinding, the level staff is called a stadia rod.
Modern automatic level in use on a construction site. A level is an optical instrument used to establish or verify points in the same horizontal plane in a process known as levelling. It is used in conjunction with a levelling staff to establish the relative height or levels (the vertical separation) of objects or marks.
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Combining a spirit level with an optical telescope results in a tilting level or dumpy level. [5] These leveling instruments as used in surveying to measure height differences over larger distances. A surveyor's leveling instrument has a spirit level mounted on a telescope (perhaps 30 power) with cross-hairs, itself mounted on a tripod. The ...