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This bi-rola chart protractor turns the tedious task of plotting into child’s play. It virtually eliminates the need for other devices except a pencil. Plotting a course is as simple as laying the protractor along your course line and aligning the compass disk. Laying off courses, bearings, distances and loran interpolation is so easy you can forget about other methods. Corrections can easily be made for variation and deviation. The body of the contractor has scales for nautical miles, millimeters and loran interpolation.