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Surveyor's view of the levelling rod with the crosshair. This indicates a reading of 1.422 m, interpolated between the 1.420 m and 1.430 m marks. Rods come in two classes: Self-reading rods (sometimes called speaking rods). Target rods. Self-reading rods are rods that are read by the person viewing the rod through the telescope of the instrument.
The rod may be equipped with a target to increase the readable range of the rod. When the target is equipped with a Vernier scale measurements to the thousandths of a foot are possible. For readings less than 7 ft the target is attached on the bottom section of the rod and adjust by signals from level operator until the target is inline with ...
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 ...
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The level must be horizontal to get a valid measurement. Because of this, if the horizontal crosshair of the instrument is lower than the base of the rod, the surveyor will not be able to sight the rod and get a reading. The rod can usually be raised up to 25 feet (7.6 m) high, allowing the level to be set much higher than the base of the rod.
Common levelling instruments include the spirit level, the dumpy level, the digital level, and the laser level. Levelling staff – specialized measuring stick or vertical staff used with the dumpy level, held by a second person while the operator of the level looks through it and takes readings off of the staff. Also call a rod. Reduced level ...
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