#### Pseudocolumns

Expressions in the using clause of a plot statement can refer to additional bookkeeping values in addition to the actual data values contained in the input file. These are contained in "pseudocolumns".

         column(0)   The sequential order of each point within a data set.
                     The counter starts at 0 and is reset by two sequential blank
                     records.  The shorthand form $0 is available.
         column(-1)  This counter starts at 0 and is reset by a single blank line.
                     This corresponds to the data line in array or grid data.
         column(-2)  The index number of the current data set within a file that
                     contains multiple data sets.  See `index`.