This ruler can be used to measure or plot latitude/longitude coordinates, UTM/MGRS/USNG coordinates, and to measure distances in either meters or miles. On the front side, the ruler has minutes and seconds on one edge and decimal minutes on the other edge, allowing you to use either notation. On the back side, the ruler has distance in meters on one edge, and distance in either miles on the other edge. Latitude is measured directly with the ruler. But, since a degree of longitude covers a shorter distance as you move towards the poles, the ruler is used on a diagonal to measure longitude.