@classmethod
def _calculate_mixing_ratio(cls, dewpoint_temp, pressure):
    """Calculates the mixing ratio from dewpoint temperature and pressure measurements.

        Requires the dewpoint temperature to be in celsius andthe pressure to be in hPa, which
        is the same as millibars.
        """
    e = 6.11 * 10 ** (7.5 * dewpoint_temp / (237.7 + dewpoint_temp))
    mixing_ratio = 621.97 * (e / (pressure - e))
    return mixing_ratio
