A novel instrument for use in chartwork has been devised combining a ruler with the principle of the square Douglas protractor, and permitting immediate indication of direction to be read without ambiguity. A prototype of this instrument, which will probably be known as the Harries Course and Bearing Indicator, is illustrated in Fig. 1. It is constructed of Perspex, and the basic ruler component has engraved upon it a long double-ended arrow, emphasized as the line AA in the illustration. Centrally pivoted above this arrow is an approximately rectangular ‘aligning plate’, B, on which are engraved equally-spaced lines, C, parallel to the 180°/360°, or north /south, line of a circular compass rose.

To obtain the direction of a course laid off on a chart, the bevelled edge, D, of the ruler is placed along it. The aligning plate is then rotated until the north/ south lines on it are seen to be parallel to any adjacent meridians (Fig. 2). The true course can then be read off directly from that degree of the compass rose lying directly over the appropriate arrow head—an action which can be carried out on a folded map or chart held on the knee.