Pre-existing Variables

Pre-existing variables are accessed by using their file names in an
expression; e.g.

     PLOT(price / earnings);

where 'price' and 'earnings' are files that exist in the current
subdirectory and whose structure conforms to the DAN data record
format.  This type of file may have been created during a previous
execution of DAN or by a user written program (see Data Files
Format section in the manual for the exact structure of DAN's data
records).
