Weems & Plath GPS Plotter. Transfer GPS coordinates to your chart easily and accurately. This plotter works like a set of sturdy parallel rules, but has sets of holes for pencil points, allowing you to transfer latitude and longitude from scales on the sides and bottom of the chart to anywhere on the page. These rules dont â€œwalkx9D like standard instruments, but move directly horizontally or vertically across the chart. 15-1/2"L.