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The American-style navigation plotter/protractor is suitable
for lower latitudes where the meridians of longitude are more
parallel to each other. In northern latitudes, where the meridians
slope toward each other, these plotters become more difficult to
use due to visual illusions (it's harder to line the plotter up
with the meridians). In northern latitudes, VFR aviators tend to
prefer the parallel-rule plotter (the "Douglas protractor") for
measuring tracks.
ATP's Douglas Protractor is able to accurately measure a track on any chart because it can be centered easily between converging meridians. The grid of parallel lines allows any track to be offset from another track, and the graduated scale along the edge of the protractor is divided into 1:500,000 scale nautical miles for use when scaling distances on the chart. Manufactured and distributed in Canada. For more information, see AeroTransport Publications |