Abstract: In a cathode ray tube display system, correction factors for X and Y position, astigmatism, focus and shading are recorded for preselected locations in digital memory circuits. Those correction factors bordering the actual beam position are selected and are converted to analog form. The correction factors applied to the system are determined by analogue interpolation, that is, the correction factors are combined in proportion to the proximity of the beam relative to those preselected locations where the correction factors were recorded. Use is made of resistance ladders and multiplexers in the interpolation circuits.