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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 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.
The Y level or wye level is the oldest and bulkiest of the older style optical instruments. A low-powered telescope is placed in a pair of clamp mounts, and the instrument then leveled using a spirit level, which is mounted parallel to the main telescope. The term dumpy level (also builder's level) endures despite the evolution in design. They ...
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 ...
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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Stadia marks on a crosshair while viewing a metric levelling rod. The top mark is at 1.500 m and the lower is at 1.345 m. The difference between the rod readings is 0.155 m, yielding a distance to the rod of 15.5 m. A typical surveyor's instrument reticle has two pairs of stadia marks. One pair are on the horizontal centreline and the other on ...