The invention relates to an instrument facilitating the plotting of a course on a chart, map and the like, said instrument comprising a graduated lens and a pointer movable relative to said lens. The novel matter of the invention resides in that the lens is formed as a convex lens and provided with a peripheral support ring defining underneath said lens a space for the pointer. The support ring is at least partly made from a material which prevents sliding movement of the instrument on the chart or map.
An improved sensor magnifying glass apparatus having a magnifying glass element (1) held in a holder element (4) and comprising a cylindrical portion (2) with a superposed convex curved lens portion (3) that is rotationally symmetrical with the cylinder axis (19). A plotter coil (11) is secured to the cylindrical portion (2) in the region between that portion's circumferential face and the course of a peripheral light ray (20') through the cylindrical portion (2) that enters the lens portion (3).
