page_title: Level staff
section_title: Classes of rods
hierarchical_section_title: Level staff / Classes of rods
context_page_description: 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. It cannot be used without a leveling instrument.
context_section_description: 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 graduations are sufficiently clear to read with good accuracy. Target rods, on the other hand, are equipped with a target. The target is a round or oval plate marked in quarters in contrasting colours such as red and white in opposite quarters. A hole in the centre allows the instrument user to see the rod's scale. The target is adjusted by the rodman according to the instructions from the instrument man. When the target is set to align with the crosshairs of the instrument, the rodman records the level value. The target may have a vernier to allow fractional increments of the graduation to be read.
  Digital levels electronically read a bar-coded scale on the staff. These instruments usually include data recording capability. The automation removes the requirement for the operator to read a scale and write down the value, and so reduces blunders. It may also compute and apply refraction and curvature corrections.
caption: 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.