GB404818A - An improved plotting device - Google Patents

Abstract

404,818. Protractors. WATSON, C. E. H., Public Works Department, Whangarei, New Zealand. Feb. 22, 1933, No. 5463. Convention date, Oct. 21, 1932. [Class 97 (iii).] A protractor for use in plotting cross sections comprises a semi-circular plate 1, Fig. 7, with scale divisions extending outwards from zero at the centre of the diametral edge 2 and angular divisions on the curved edge extending in both directions from a zero on the perpendicular through the zero of the diametral edge. Means are provided to enable the protractor to be pivoted about the zero on the diametral edge and may comprise a notch, a fixed pin, a pin which may be moved from a position flush with the surface of the protractor to a working position by rotation or sliding, or a pin 20 clamped in a spring arm 17 so as to be normally held away from the drawing surface. A series of lines parallel to the line joining the two zeros may be drawn through the graduations on the edge 2 or a scale 4 parallel to the edge 2 provided. In a modification, Fig. 6, a transparent triangular or other shaped plate has a straight edge 2 and a semicircular mark, both graduated as in Fig. 7. A pivot pin 6a is fixed on an arm 17a pivoted to the plate at 30 and having a cross piece 27 with studs 28 adapted to engage cavities 29 when the pin is in working position. An aperture 39 enables a mark to be made adjacent the zero on the semicircular mark. In an alternative form, the plate is opaque and has a cut-away portion along the edge of the semicircular mark.