Abstract: Cathode ray tube apparatus including compensation (14) for the vertical component of terrestrial and of other ambient magnetic fields (15). The compensation is achieved by the generation of an opposing vertical magnetic field by energization of the degauss coil (11, 12) in the apparatus. Two embodiments are described: one applies a continuous direct current (21) after the degaussing operation and the other applies a direct current component coincident with the degaussing signal to permanently magnetize components of the apparatus. The magnitude and polarity of the compensation provided may be variable.