The graphometer was invented in Paris around the end of the XVIth century by Philippe Danfrie. It was an adapted form of the azimuth plate or simple theodolite. It was described as "a sighting compass, an instrument designed to measure angles approximatively". It consists of a graduated semicircle with two alidades (or rulers with sights), one of which is fixed to the semicircle, the other which slides along the scale.
The semicircle of this instrument with fixed pinnules 21 cm in diameter has half-degree divisions. The movable alidade has a vernier that reads to ten arcminutes.
The large central compass, present in this model, means the instrument can also be used for surveying purposes, unlike the older designs of Danfrie.
Inscribed are the words Sevin Paris: Pierre Sevin was a manufacturer of mathematical, topographical and astronomical instruments who worked in Paris between 1665 and 1683.
J.A. Bennett (1987), pp. 50, 75.
M. Daumas (1953), p. 103.
M. Holbrook (1992), pp. 35 and 74.
G. L’E. Turner (1991), p. 198.