Breton_plotter
Breton plotter
Navigational instrument
A Breton plotter (French: Rapporteur Breton), also known as a Portland course plotter or Weems protractor named after later manufacturers producing similar devices, is a navigational instrument used for nautical navigation with charts.
The Breton plotter contains a ruler with a rotating protractor that serves as a compass rose, allowing navigators to plot a course on charts by aligning the North of the ruler with the North of the chart.[1]