code: def _add_converted_units(self, dataframe, parameter, key='VALUE'):
          
          convert_unit = self.parameters.get_converter(parameter)
          try:
              log.debug("Adding unit converted DATA_VALUE to the data")
              dataframe[key] = dataframe['DATA_VALUE'].apply(convert_unit)
          except KeyError:
              log.warning("Missing 'VALUE': no unit conversion.")
          else:
              dataframe.unit = self.parameters.unit(parameter)
docs: Add an additional DATA_VALUE column with converted VALUEs