Magnetometer n. : An instrument for measuring the intensity of magnetic forces; also, less frequently, an instrument for determining any of the terrestrial magnetic elements, as the dip and declination.

Example:
how do you build a homemade Magnetometer to study how the earths magnetic fields are different by solar storms

Taxonomy
magnetometer, magnetic field, measure, fluxgate magnetometer, coil, signal, frequency, sensor, measurement, instrument, SQUID magnetometers, Earth, cesium magnetometer, flux, photon, proton magnetometer, SERF, nT.

Defination from the web:
magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ... A magnetometer can also be used by satellites like GOES to measure both the magnitude and direction of a planet's or moon's magnetic field. ...