Specify a corresponding
vertical coordinate when using the X variable. This vertical coordinate
can be specified with the Y, YC, MIDPOINT, or SUBGROUP variables,
depending on the type of graph that you are annotating.
The X variable uses
the units that are specified in the XSYS variable. If you use XSYS='2'
and the data axis is typed as character, use the XC variable instead
of the X variable.
If the value of the
X variable is missing for a function that requires it, the value of
the XLAST variable is used with nontext functions and the value of
the XLSTT variable is used with text functions.