BBC Two until 23 October 2012, via the Ceefax teletext service. The BBC also offers audio description on some popular programmes for visually impaired-viewers as well as sign language interpretation on some of its programmes for deaf and hard-of-hearing viewers. The percentage of the BBC's total television output with audio description available is 10%, having been increased from 8% in 2008. Originally, programmes from BBC Two were shown in high definition on the dedicated BBC HD channel, alongside programmes from BBC Three and BBC Four, as well as some select series from CBBC and CBeebies. However, in plans outlined by the director
Teletext economic Teletext system with 1971 technology. However, as low cost was essential to the project's long term success, this obstacle had to be overcome. Meanwhile, the General Post Office (GPO), whose telecommunications division later became British Telecom, had been researching a similar concept since the late 1960s, known as Viewdata. Unlike Teledata which was a one-way service carried in the existing TV signal, Viewdata was a two-way system using telephones. Since the Post Office owned the telephones, this was considered to be an excellent way to drive more customers to use the phones. In 1972 the BBC demonstrated their system,