XAXIS = varname;        Specify name of file used for X axis

The XAXIS control specifies the name of the file used for the X
axis of subsequent plots.  'varname' must be the name of a
previously created data file or 'T'.  All subsequent plots will be
produced with the specified data file determining the values along
the X axis.  The START, BIAS, and DUR controls specify the subset
of the XAXIS data file to be used.

Plots versus the implicit loop parameter (normally time) can be
reenabled by entering:

    XAXIS = T;

Be sure to set appropriate XMAX and XMIN values before the plots are
generated.  Default XMIN and XMAX values, as set in DAN's 'Plot
Controls' form or with control statements in the algorithm, are only
in effect when a variable is used for the X axis.
