x_samples = seasons_between_dates(xmin, xmax) + 1
set samples x_samples, 100
+# NOTE that the ticks will be placed at the beginning of months regardless of
+# the day of the month of xmin. See:
+# https://stackoverflow.com/questions/42212039/gnuplot-xtic-labels-mispositioning-with-dates
set xtics xmin,three_months
set terminal qt 0