The basic trigometre design consists of two graduated arms pivoting at the end of a fixed base. In Danfrie's version, each arm carries a graduated arc for measuring the angles formed with the fixed base. The distance to a point can be computed using the similarity of triangles or the sine theorem. Instrument was named by Philippe Danfrie (c. 1532-1606) in 'Traicté de l'usage du Trigometre avec le quel on peut facilement mesurer sans subjection d'Arithmetique' (Paris, 1597).
Original tooled leather case and companion scales.