These rulers are useful for working with a GPS receiver and paper maps. Each ruler is designed for a specific map scale. You must use the ruler that matches the scale of the map. On the front side, the rulers are marked in minutes and seconds on one edge and decimal minutes on the other edge, allowing you to use either notation. On the back side, the rulers are marked in meters on one edge, and miles on the other edge. The “Explorer Set” contains twenty-two common map scales that should cover most of the maps you’re likely to encounter in land navigation. Scales included: * 1:24,000 * 1:25,000 * 1:50,000 * 1:62,500 * 1:63,360 * 1:69,500 * 1:77,000 * 1:80,000 * 1:84,000 * 1:100,000 * 1:125,000 * 1:126,720 * 1:150,000 * 1:156,000 * 1:160,000 * 1:182,000 * 1:200,000 * 1:250,000 * 1:300,000 * 1:320,000 * 1:400,000 * 1:500,000