W&P 155 These navigator's parallel rulers are inscribed with full 180º protractor markings. The middle of the bottom edge forms the protractor center when the arms are closed. This tool combines the essential features of a protractor plotter and a basic parallel ruler. Allows courses to be measured from a convenient meridian. Made of extra strong, crystal clear acrylic.
Weems & Plath has patented the Bi-Rola for its vertical and horizontal rolling motion to simplify course plotting calculations, while the unique radial arm allows you to automatically include compass corrections in your plotting. The Bi-Rola is the most completely self-contained device in its class, and will withstand years of use due to its brass and heavy duty plastic construction.