The number is displayed on the screen of a cathode-ray tube, the characters being directly written by movement of the spot. The effect of a steady display is created by a high speed repetitive traverse over the outlines required, a black-out being effected between the characters and on the fly-back.The spot control is achieved by a combination of alternating figure-producing potentials and steady spacing or layout potentials. The former are provided by a common “figure generator” which uses a continuously rotating multi-unit variable condenser to modulate a 500-kc/s supply, generated by a built-in oscillator. The outputs are rectified to give the X and Y component potentials of the integers 1, 2… 0 at an audio frequency.A layout selector connects the tube in sequence to the required figure potentials and adds the steady potentials to locate each in its appropriate position in the frame. The application to “calling line identification” is described in an Appendix; other applications and developments are outlined.