axes[-1, 0].annotate('', xy=(0, ypos), xytext=(length, ypos), xycoords=(
    'data', 'axes fraction'), textcoords=('data', 'axes fraction'),
    arrowprops=dict(arrowstyle='<|-'))
axes[-1, 0].annotate('{0} data units'.format(length), xy=(length / 2.0,
    ypos), xytext=(0, 5), xycoords=('data', 'axes fraction'), textcoords=
    'offset points', ha='center', va='bottom')
plt.show()
Help with making a big subplot look nicer and clearer