This GPS parallel rule, in a compact size, is particularly suited for use on modern small chart tables. The primary purpose of the Paralock Plotter is to enable the transfer of GPS positions rapidly, easily and accurately to and from any paper chart. Made of sturdy, clear acrylic for maximum chart visibility. It has graduation s so it can be used as a protractor to determine compass bearing. It also has a ruler across the bottom, making it is easy to take distances and transfer th em to a mileage scale.