The set xmtics command converts the x-axis tic marks to months of the
year where 1=Jan and 12=Dec.  Overflows are converted modulo 12 to months.
The tics are returned to their default labels by unset xmtics.  Similar
commands perform the same duties for the other axes.
Syntax:
     set xmtics
     unset xmtics
     show xmtics
The same syntax applies to x2mtics, ymtics, y2mtics, zmtics and
cbmtics.
See also the set format (p. 
) command.