The most exciting new plotter we've seen! A friend of ours reports he was taking a Coast Guard navigation exam with 22 other people. A few of the applicants had the bi-rola rule. According to our friend, they "really burned up" the plotting portion, and finished long before the others. It is constructed of heavy duty plastic with brass rollers, and is practically indestructible. The plotter moves up and down like a normal rolling plotter. By tilting it though, it can be moved sideways without disturbing its orientation. This allows a course line to be moved anywhere on the chart's surface with ease. A swing radial arm has 3 loran interpolator scales, and when used in conjunction with the body, serves as a large divider for measuring long distances. The arm also allows courses to easily be measured in true or magnetic. The roller body itself has protractor markings, and a nautical mile scale. Dimensions are: Length 13-7/8 in., Width 2-5/8 in., Thickness 1 in. Weight is 12 oz. The unit comes packaged in a durable, vinyl protective pouch. We strongly recommend this plotter.