GREG includes two basic character sets generated by software. The SIMPLEX set is the default for interactive devices. The DUPLEX set is nicer, but slower and requires a higher resolution device ; typically it will be reserved for quality publication plots. Except for the aspect of the characters, there is no difference between the SIMPLEX and DUPLEX fonts, that is the sizes and proportional spacings are identical. The default font may be overridden by SET FONT SIMPLEX or DUPLEX. In each quality, complete roman, script and greek alphabets are available. Special characters are used to access specific symbols not available on a keyboard, including mathematical and astronomical symbols. The table of correspondence is shown in Section 7. As a rule, astronomical symbols are obtained in the greek character set, and mathematical symbols in the script set, the roman set having of course an exact correspondence with the keyboard, except for the double quote (key not available because of SIC character handling) which is obtained using the counter-quote, degree symbol which is obtained using the circumflex symbol, and the back-slash which is not available.