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 in the USA. A few other services were offered by some large-market TV stations in the US throughout the 1980s, such as Metrotext from KTTV in Los Angeles and KeyFax from WFLD in Chicago. Despite this, the system never caught on in the USA partly due to EIA-608 being deployed for captioning before Teletext was introduced and the higher cost of Teletext receivers. In the 1980s a similar system called Telidon was developed in Canada by the Department of Communications. It used a simple graphics language that would allow a more complex circuit in the TV to decode not only