Original Vortrack
I used to use these in the day when I only had a King KX155 (single VOR with flip-flop frequencies). They were invented by Gordon Wansborough-White (a sailor who lived on a barge, I remember) who used to use them to run the GNAV competition at White Waltham - so the present organisers of the competition might still have a supply or know where. Basically you fix a larger compass rose (self-adhesive) on top of the vOR on your map, clip press-studs through the centre (makes a whole in your map, but you leave the studs in), and then affix the arm on top. Dial up the VOR, swing the arm so the numbers line up with the radial the VOR says you were one - and you are on the line of the arm. If you've DME too, you read off exactly where you are along the scale (half-million maps of course). If no DME use two VORs and get perfect intersection. Very clever and the GNAV comp was based around what was a series of diversions planned in mid-air by using this gizmo. Hope you find it - it was a great invention for a basic avionic aircraft (pre GPS).