Marine radar viewing unit Type 7004/A (serial no. 435), with 15" screen, from a harbour control radar, used at Thames Navigation Service, Gravesend until 1963.

All functions in the display unit circuits are initiated by the trigger pulse from the receiver unit. The pulse triggers a flip-flop which produces a square pulse of duration approximately equal to the duration of the time base in use. This square pulse is then used to operate the time base, calibrator and brilliance circuits. A video amplifier is included in the unit and the limiter circuit prevents the mixer video, calibrator and heading marker signals from producing excessive brilliance of the trace should any of these signals be super imposed on another.