Large Pinnules Graphometer, Signed

Function: To measure angles on the field. Description: This device consists of a semi-circle and two alidades with pinnules. The semi-circle, usually 16 to 22 centimeters in diameter, is divided into semi-degrees. It is provided with two alidades, one fixed, directed according to the diameter, the other mobile, which can turn around the center. Their extremities are thinned out in a bevel following arcs of a circle and which, in all the positions of the alidade, coincide, one or the other, with the divided circle of the limb. In addition, they carry verniers which allow the division fractions to be evaluated. On the fixed alidade is drawn a straight line passing through the center and corresponding to the wires of the pinnules: this is what is called the “headline” of the fixed alidade; it is from this line of faith that the divisions of the limb are counted. The mobile alidade also has its lubber line, which continues beyond the pinnules and corresponds to the zero of each vernier. The limb is provided with a small compass which makes it possible to be directed on the ground. The graphometer is equipped with a shell knee that allows it to be oriented in all directions. Beware, the needle is not on its axis.