docs: def dew_point_temperature(self):
          """Return the dew point temperature in ºC for the last measurement.
  
          For sensors implementing temperature and humidity values.
          Extracted from the HTU21D sensor spec sheet."""
          if self.sample_ok:
              temperature = self._get_value_opc_attr('temperature', 3)
              humidity = self._get_value_opc_attr('humidity', 3)
              if temperature is not None and humidity is not None:
                  # Calc dew point temperature in celsius
                  coef_a, coef_b, coef_c = 8.1332, 1762.39, 235.66
                  part_press = 10 ** (coef_a - coef_b / (temperature + coef_c))
                  dewp = - coef_c
                  dewp -= coef_b / (log10(humidity * part_press / 100.) - coef_a)
                  return dewp
          return None