@classmethod
def _create_bits_by_thousand_rocks(cls, figure, data_by_year, shifts, bits):
    """Bits by thousand rock mass."""
    bit_by_rock = figure.add_subplot(224)
    bits_by_thousand_rocks1 = bits[0] / (data_by_year[shifts[0]].rock_mass /
        1000)
    bits_by_thousand_rocks2 = bits[1] / (data_by_year[shifts[1]].rock_mass /
        1000)
    bit_by_rock.plot(data_by_year[shifts[0]].month, bits_by_thousand_rocks1,
        marker='D', markersize=4)
    bit_by_rock.plot(data_by_year[shifts[1]].month, bits_by_thousand_rocks2,
        marker='D', markersize=4)
    bit_by_rock.legend(['Смена 1', 'Смена 2'])
    bit_by_rock.set_ylabel('коронок / 1000м³ горной массы')
    bit_by_rock.set_xlabel('месяцы')
    bit_by_rock.grid(b=True, linestyle='--', linewidth=0.5)
    bit_by_rock.set_title('Коронок на тысячу кубов горной массы.')
