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(physics) An instrument used to measure the intensity and direction of a magnetic field, especially at points on the Earth's surface; sometimes used as metal detector.

NASA caption for this image: "... The two Magnetic Field Experiment (MAG) sensor suites can be seen on the 4-meter-long dedicated magnetometer boom in the foreground. The MAG boom is deployed in flight at the outer end of one of the spacecraft's three solar arrays. The outboard sensor suite consists of a Fluxgate Magnetometer (FGM) visible just above the 2 Advanced Stellar Compass (ASC) light baffles that look outward at a slight angle. The inboard MAG sensor suit is identical, but rotated 180 degrees and located 2 meters away. When deployed, the two sensor suites will be about 10 and 12 meters from the center of the spacecraft. The spacecraft is shown in launch configuration with solar arrays and MAG boom stowed. Image credit: NASA/JPL-Caltech/LMSS"

(physics) An instrument used to measure the intensity and direction of a magnetic field, especially at points on the Earth's surface; sometimes used as metal detector.

Helium vector magnetometer (HVM) of the Pioneer 10 and 11 spacecraft

(physics) An instrument used to measure the intensity and direction of a magnetic field, especially at points on the Earth's surface; sometimes used as metal detector.

Artist generated diagram showing the location of various instruments. MAG is on the lower right of this graphic