higher resolution graphics. The proposed higher content levels included geometrically specified graphics (Level 4), and higher-resolution photographic-type images (Level 5), to be conveyed using the same underlying mechanism at the transport layer. No TV sets currently implement the two most sophisticated levels. Decoders The Mullard SAA5050 was a character generator chip used in the UK teletext-equipped television sets. In addition to the UK version, several variants of the chip existed with slightly different character sets for particular localizations and/or languages. These had part numbers SAA5051 (German), SAA5052 (Swedish), SAA5053 (Italian), SAA5054 (Belgian), SAA5055 (U.S. ASCII), SAA5056 (Hebrew) and SAA5057 (Cyrillic). The type of decoder circuitry is sometimes marked on televisions as CCT (Computer-Controlled Teletext), or ECCT (Enhanced Computer-Controlled Teletext). Besides the hardware implementations, it is also possible to decode teletext using a PC and video capture or DVB board, as well as recover historical teletext from self-recorded VHS tapes. The Acorn BBC Micro's default graphics mode (mode 7) was based on teletext display, and the computer could be used to create and serve teletext-style pages over a modem connection. With a suitable adapter, the computer could receive and display teletext pages, as well as software over the BBC's Ceefax service, for a time. The Philips P2000 home computer's video logic was also based on a chip designed to provide teletext services in TVs. Uses Interactive teletext Some TV channels offer a service called interactive teletext to remedy some of the shortcomings of standard teletext. To use interactive teletext, the user calls a special telephone number with a push-button telephone. A computer then instructs them to go to a teletext page which is assigned to them for that session. Usually, the page initially contains a menu of options, from which the user chooses using the telephone keypad. When a choice has been made, the selected page is immediately broadcast for viewing. This is in contrast with usual teletext where the user has to wait for the selected page to be broadcast. This technology enables teletext to be used for games, chat, access to databases, etc. It overcomes the limitations on the number of available pages. On the other hand, only a limited number of users can be serviced at the same time, since one page number is allocated per user. Some channels solve this by taking into account where the user is calling from and by broadcasting different teletext pages in