The set xmtics commands 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 set noxmtics. Similar
commands perform the same duties for the other axes.
Syntax:
set xmtics
set noxmtics
show xmtics
The same syntax applies to x2mtics, ymtics, y2mtics, and zmtics.
See also the set format command.