Abstract: A navigational aid to define the direction relative to a reference direction of a line between two designated points on a chart of the kind comprising a base surface for the chart, a rotatable direction indicating member having one or more directional indices and being displaceable relative to the base surface carried by two mutually cooperating support means of which a first one is movable relative to the base surface in one direction along a stationary rectilinear guide means, and the second one is movable in a direction perpendicular thereto along a rectilinear guide means carried by the first support means. In a device according to the invention said first movable support means constitutes a first rectangular transparent frame, carried in guide means located at each one of two opposite edges of the frame by each one guide rail which is stationary relative to the base surface and along which this first frame is movable in said one direction.