SCALEX (expr);              Determine X axis scaling

The SCALEX procedure causes automatic scaling to be done for the X axis
based on the minimum and maximum values for 'expr'.  This procedure is
a faster and more convenient way of doing the following:

    XMIN = MIN(expr) & XMAX = MAX(expr);

This procedure is normally not necessary; use it only if you are
plotting one variable versus another (i.e. an 'XAXIS = varname;'
statement is in effect).
