When scientists need to determine the power or the direction of a magnetic field, whether on Earth or in space, they use a magnetometer. These scientific instruments also are used to calibrate both electromagnets and permanent magnets, as well as to indicate whether a material is magnetized.
To determine the magnetic field of the Earth, two styles of magnetometers are commonly used: absolute and relative. The former are calibrated with respect to their own known settings, and the latter by an accurately quantified magnetic field.
The first magnetometer is thought to be the version designed by German scientist Carl Friedrich Gauss in 1832, a primitive device made up of a permanent magnet suspended in midair by a fiber. Although it lacked sophistication, he was able to use the model to formulate his own law of magnetism.
Magnetometers are used in many different fields; they are used in geophysics, archaeology, in the oil and gas industry and for space exploration.