For drawing accurate maps in the field. Note: do not overtighten on tripod -- will become impossible to remove.
Use with an alidade for sighting to features and drawing rays. Alidades range from the simple style shown in the photo, or a telescopic alidade, or even an improvised alidade such as a three-sided engineer's scale. Oriented with a compass -- Brunton recommended for accuracy and inclusion of a bubble level.
Suitable tripod: Plane Table Tripod