This Map Measurer is designed to measure straight and curved distances accurately on maps of all types. Primarily designed for military, hikers, motorists and cyclists, it has also proven useful for architects, surveyors, schools and offices as its primary function is to measure distances of curved lines. Perfect for roads, tracks, creeks and rivers. Simply set the pointer to ZERO on the scale, then trace the route or distance to be measured with the wheel. The pointer indicates on the dial the exact distance measured in proportion to the scale of the map.