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.
Examples:
set xmtics
set ymtics
set zmtics
set x2mtics
set y2mtics
set noxmtics
etc.
show xmtics
etc.
See also the set format command.