(fl∂ks’ gāt mag n∂ tam’ ∂t ∂r) An instrument capable of detecting changes in the magnetic field of the order of 0.2 nanotesla. See Figure F-16. The magnetometer measures the magnetic field component along the axis of its core and must be oriented with the field if the total intensity is to be measured. This is usually accomplished by using three mutually perpendicular fluxgate instruments and servomechanisms that vary the orientation to minimize the magnetic field in two of these, thus maximizing the field for the third. Compare proton magnetometer, optically pumped magnetometer, and Squid cryogenic magnetometer.