Read a surveyor's leveling rod by first making sure the optical instrument is completely level, having an assistant hold the rod straight and steady in the location being studied, and placing the optical instrument's crosshairs directly on the rod. The reading on the rod corresponds to how much lower the point is relative to the optical instrument's elevation.
A surveyor's leveling setup includes three basic components: the optical instrument, a tape measure and the calibrated leveling rod itself. The optical instrument is essentially a small refracting telescope mounted on a sturdy tripod base. Most modern levels feature multiple spirit levels on the telescope for ensuring the instrument is absolutely level. Surveyors determine the distance between the telescope and the rod using the retractable tape measure.
There are two types of surveyor's levels: the more common modern dumpy level and the older Wye level. A dumpy level is a small refracting telescope with internal cross hairs that is permanently attached to its mounting apparatus. A Wye level is very similar to a dumpy level, but its telescope component is removable and not permanently attached to the mount. The automatic level is a subtype of dumpy level that features internal mechanisms that correct for minor errors when the instrument is not perfectly level.