A type of cold-cathode ionization gauge in which a discharge is maintained between two electrodes with a potential difference of a few kilovolts. An axial magnetic field is also applied to cause electrons to move in spiral paths and increase the ionization current and sensitivity. This type of gauge is used in the range 10−3−10−t torr. It was invented in 1936 by the Dutch physicist Frans Penning (1894–1953).