Teletext and to pad out the fixed packet. The vertical caption position is determined by the packet address. In the case of the Ceefax and ORACLE systems and their successors in the UK, the teletext signal is transmitted as part of the ordinary analog TV signal but concealed from view in the Vertical Blanking Interval (VBI) television lines which do not carry picture information. The teletext signal is digitally coded as 45-byte packets, so the resulting rate is 7,175 bits per second per used lines (41 7-bit 'bytes' per line, on each of 25 frames per second). A teletext page comprises
Teletext Ltd. in conjunction with ORACLE, as an auxiliary teletext provider for Channel 4 from 1982. 4-Tel occupied pages 410-469 within ORACLE's page space. When ORACLE lost its licence and was replaced by Teletext Ltd in 1993, 4-Tel moved to its own page space on pages 300-399 (effectively its own magazine). Channel 4 enlisted Intelfax to run the service. In 2002, 4-Tel was renamed FourText. In addition, FourText also launched on digital television. In 2003, Channel 4 ended their contract with Intelfax and contracted out the service to Teletext Ltd. The new service was named Teletext on 4 and operated on pages