Graphometer

A portable surveying instrument with sights and a graduated semicircle for measuring horizontal angles. It was commonly used to establish directions and map land.

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Alidade: A straightedge or sighting device used to establish a line of sight and read directions on a graduated instrument. The graphometer’s sights serve as alidades, aligning the instrument with survey points.
Plane surveying: Surveying that treats the surveyed area as a plane because Earth’s curvature is negligible at its scale. Graphometers were used within this practical framework for measuring small areas.
Cadastral surveying: Surveying that establishes property boundaries and records land parcels. Graphometers helped measure boundary directions and parcel geometry.
Surveying compass: A field instrument that determines directions using a magnetic needle and an angular scale. It measured directions magnetically, unlike the graphometer’s direct sighting between points.
Graduated circle: A circular scale marked with angular divisions for measuring directions or angles. Its semicircular scale supplies the angular readings taken with the graphometer.
Surveying: The practice of measuring and mapping the positions, distances, and elevations of points on Earth’s surface. The graphometer is a field instrument developed for this broader practice.
Topographic surveying: Surveying that records terrain features and their positions for maps. Its angle measurements supported the location of features in field mapping.
Dioptra: An ancient Greek surveying instrument used for sighting and measuring angles. It is an earlier instrument in the history of angular surveying.
Horizontal angle: The angle between two directions projected onto a horizontal plane. This is the quantity a graphometer is designed to measure.
Bearing (navigation): The horizontal direction from one point to another, usually expressed as an angle from a reference direction. Graphometer observations can establish bearings between survey stations.