An instrument to measure the strength of a magnetic field. 'Gauss' refers to the cgs unit of magnetic flux density (= 10-4 tesla) named after polymath Carl Friedrich Gauss (1777-1855). The 'Oe' on the dial refers to the cgs unit of magnetic field strength, the oersted, named after H.C. Oersted (1777-1851). Effectively, the two are the same in free space.
A slim probe contains a ribbon of semiconductor carrying a steady longitudinal current. A perpendiclar magnetic field induces a small emf across the ribbon proportional to the strength of the field, an effect discovered by Edwin Hall in 1879. This is greatly amplified to provide a reading on the meter. To account for amplifier drift, the unit is supplied with a calibration source consisting of two permanent magnets.
