Viewdata

Design

Viewdata offered a display of 40×24 characters, based on ISO 646 (IRV IA5) – 7 bits with no accented characters. Originally, Viewdata was accessed with a special purpose terminal (or emulation software) and a modem running at ITU-T V.23 speed (1,200 bit/s down, 75 bit/s up). By 2004, it was normally accessed over TCP/IP using Viewdata client software on a personal computer running Microsoft Windows, or using a Web-based emulator.

Keypad symbols: the sextile and the square

Viewdata uses special symbols already widely available on telephone keypads: the ⚹ "star key" and the ⌗ "square key", as formally recommended by the International Telecommunication Union. The ASCII asterisk (*) and number sign (#) are sometimes used instead because they are regular symbols on computer keyboards, although they do not match the ITU specification. On telephones, use of the number sign (hash symbol) has become the norm rather than the exception.

These symbols appear as U+26B9 ⚹ SEXTILE and U+2317 ⌗ VIEWDATA SQUARE in the Miscellaneous Symbols and Miscellaneous Technical Unicode blocks, respectively. The sextile was added due to its use in astrology, and the square had previously appeared in the BS_Viewdata character set, as a replacement for the underscore.

In 2013, the German national body submitted a Unicode Technical Committee proposal to align the Unicode reference glyphs with the ITU specifications for these symbols, and annotate them as telephone keypad symbols on the code charts. As of 2019 (Unicode 12.1), these changes have not been accepted/implemented.