"The Earth Magnetometer is used to map the earth's magnetic field. It shows the variation from place to place down to a resolution of .01 milligauss (= 1 nanotesla, or 1 gamma), which is about 1\/500 percent of the earth's field strength. Because the earth's field fluctuates by typically 3-30 nanoteslas per hour, a resolution better than 1 nanotesla will not be of much additional benefit. Until now, resolution of 1 nanotesla or .01 milligauss could be achieved only with very expensive, heavy, and high-power-consuming magnetometers such as proton-, overhauser-, and cesium- types."