The Association must define and communicate its officially accepted symbols to other organizations and professionals, including publishers, dictionary makers, computer-systems specialists, and programmers. Accordingly, it was decided that each accepted symbol or diacritic should be assigned a unique numerical equivalent, independent of computer-coding conventions, and a unique name which provides a mnemonic description of the character shape. Symbols that have been used in earlier versions of the IPA, but deleted in later revisions, should retain a number, and name, for reference purposes. The numerical equivalent (IPA Number) is to be regarded as a communication-interchange standard, to serve as a basis for creating computer-code translation tables from various phonetic-character-set software to the common IPA Number. This IPA Number is not implemented directly in computer format (for example, ASCII), but is expressed as a simple numerical directory of digit triples to serve as a unique reference. The IPA Number can also serve as a typesetter's guide to the Phonetic Symbol Chart. The systematic numerical listing represents the IPA symbols as presented in the Chart. Therefore, the first digit of the triple indicates the symbol category; inn for accepted IPA consonant symbols, 2nn for former IPA consonant symbols and non-IPA consonant symbols, 3nn for vowels, 4nn for segmental diacritics, 5nn for suprasegmental symbols; 6nn-8nn are reserved for future specification (e.g., for symbols for voice quality settings or for pathological speech). The digit triple 9nn has the function of an escape sequence from IPA-symbol mode into procedures definable for special applications (e.g., Roman, Greek, Cyrillic orthographies, “Comment” mode, etc.).