Proprietary Plotters

A Breton plotter (or Portland plotter) is a rotating protractor that sits directly on the chart grid. You align it with a meridian (N-S line) or parallel (E-W line) on the chart, then read the bearing directly — no need to walk to a compass rose. This makes them easier to use on a moving boat.

To plot a bearing, set the plotter to the desired angle, align it with a meridian, position the edge on your starting point, and draw the line. To measure an existing line, align the plotter edge with the line, then align the grid with a meridian and read the bearing.