The AlphaLab Earth Magnetometer weighs only 18 ounces (= 510 grams), and runs about 8 hours on the included standard 9-volt alkaline battery. It measures difference in field strength to accuracy of +/-0.5% of the difference, either for point-to-point or time-to-time measurements. In other words, if one location is 2.00 milligauss (200 nanotesla) stronger than another location, the Earth Magnetometer will indicate that difference to accuracy of +/- .01 milligauss or 1 nanotesla.
This magnetometer has a magneto-resistive sensor, which uses the spins of electrons flowing through a circuit, rather than their charge, to measure magnetic field. This type of device most closely resembles a “flux gate” magnetometer, but the magneto-resistive technology is newer, smaller, less expensive and intrinsically more stable over temperature.