Abstract: This invention is concerned with generating line symbols (e.g. straight lines, circles) on cathode ray tube displays with TV-type scans. A tube 10 has the normal line and frame deflection waveform generators 12 and 13 and a normal video amplifier 15. A symbol generator 20, 20', 20", etc. is provided for each symbol; the generators may be controlled by a computer 21 which defines the parameters of the symbol (e.g. slope and position of a straight line). Each symbol generator contains two waveform generators--line and frame frequency waveform generators synchronised by the line and frame synch pulses LSV and FSV--and a comparator which produces output pulses when the voltages from the two generators are equal. These pulses are fed to the video amplifier 15. The waveforms generated by the two generators are chosen to give the desired symbols; e.g. sawtooths for straight lines, parabolic waveforms for ellipses. The output pulses have substantially vertical leading and trailing edges.