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 semi-circle or semicircumferentors. Some 19th-century graphometers had telescopic rather than open sights.
Usage
To measure an angle, say, EKG, place the diameter middle C at the angle apex K using the plummet at point C of the instrument. Align the diameter with leg KE of the angle using the sights at the ends of the diameter. Align the alidade with the leg KG using another pair of sights, and read the angle off the limb as marked by the alidade. Further uses of the graphometer are the same as those of the circumferentor.
References
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Last updated on Wednesday January 09, 2008 at 09:04:34 PST (GMT -0800)
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