Related on Lably
Through Angle, Sight (device) and Compass
The form was introduced in Philippe Danfrie's Déclaration de l’usage du graphomètre (Paris, 1597) and the term graphometer was popular with French geodesists. The preferable English-language terms were semicircle or semicircumferentor. Some 19th-century graphometers had telescopic rather than open sights.
Le Nôtre's La theorie et la pratique du jardinage ('The theory and practice of gardening'), published in 1709, described the use of the graphometer in transferring geometric shapes from garden plans onto landscapes at a large scale.
Usage
To measure an angle, say, EKG, the diameter middle C is placed at the angle apex K using the plummet at point C of the instrument. The diameter is aligned with leg KE of the angle using the sights at the ends of the diameter. The alidade is aligned with the leg KG using another pair of sights, and the angle read off the limb as marked by the alidade. Further uses of the graphometer are the same as those of the circumferentor.