instrument that measures magnetism—either magnetization of magnetic material like a ferromagnet, or the direction, strength, or the relative change of a magnetic field at a particular location
Good to know
Magnetometers are widely used for measuring the Earth's magnetic field and in geophysical surveys to detect magnetic anomalies of various types. https://en.wikipedia.org/wiki/Magnetometer
The picosats and the mothership, OPAL, are instrumented with magnetometers to measure their attitude relative to the magnetic field. The intent is to simultaneously sample a volume of space for denser magnetic field measurements.