Breton plotter

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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. It is a ruler with a rotating rose that enables to plot a course on charts, while aligning the North of the ruler with the North of the chart.

The Breton plotter was invented by Captain , a Breton seaman who developed the plotter during his experiences teaching navigation with a Cras plotter [fr] (Règle Cras) by Jean Émile Paul Cras. Gueret was a commander in merchant vessels, served on small fishing boats, delivered private yachts and taught navigation. He later extended the use of the plotter to air navigation for small aircraft.

References[]

Further reading[]

• https://web.archive.org/web/20210712171156/https://www.cruisersforum.com/forums/f121/special-purpose-protractor-162563-2.html

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