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The development of teletext started in the UK in the early 1970's after investigation into methods of broadcasting subtitles. It was clear that it would soon be economic to build, into every television receiver, LSI circuitry to decode and to display data transmitted during the blanking intervals of the broadcast television signal. Extensive research by the BBC, the IBA and members of BREMA* led to agreement on a unified UK standard for teletext in 1974 and, after a 2 year trial, to a full public teletext service starting in November 1976.1 ,2 The evolution of this UK standard was influenced by the fundamental requirements of a practical data broadcasting service: (1) the service should provide a comprehensive range of information attractively presented, (2) access time, the delay between the viewer selecting a page and the first reception of that page,should be acceptably small, (3) data transmission should be compatible with the normal distribution network, it should have as large a service area as the colour television signal, and should not interfere with normal reception of colour television programmes,3'4 (4) the display should be easily read, (5) transmission errors should have minimnum subjective effect, (6) receivers should be low cost, (7) future options both for transmission and reception should be considered.
N. E. Tanton (Sun,) studied this question.