Abstract: A marine direction finding system is disclosed wherein a rotatable and calibrated dial is placed over a direction indicating dial of a radio direction finder. The radio direction finder indicates direction by illuminating a portion of its indicating dial. The direction of the radial signal received is referenced to a front of the boat which is calibrated as 0.degree.. The rotatable dial is preferably at least semitransparent and is calibrated at a first radius from 0.degree. to 360.degree. and at a second radius also from 0.degree. to 360.degree. but offset by 180.degree.. When a signal is received, the rotatable dial first radius marking is set to a 0.degree. marking on the direction finder in accordance with the current magnetic heading for both.