docs: def get_converter_to_specific(self, dataset=None, mass=None,
                                    to_unit=None, from_unit=None):
          """get the convertion values
  
          Args:
              dataset: DataSet object
              mass: mass of electrode (for example active material in mg)
              to_unit: (float) unit of input, f.ex. if unit of charge
                is mAh and unit of mass is g, then to_unit for charge/mass
                will be 0.001 / 1.0 = 0.001
              from_unit: float) unit of output, f.ex. if unit of charge
                is mAh and unit of mass is g, then to_unit for charge/mass
                will be 1.0 / 0.001 = 1000.0
  
          Returns:
              multiplier (float) from_unit/to_unit * mass
  
          """
  
          if not dataset:
              dataset_number = self._validate_dataset_number(None)
              if dataset_number is None:
                  self._report_empty_dataset()
                  return
              dataset = self.datasets[dataset_number]
  
          if not mass:
              mass = dataset.mass
  
          if not to_unit:
              to_unit_cap = self.cellpy_units["charge"]
              to_unit_mass = self.cellpy_units["specific"]
              to_unit = to_unit_cap / to_unit_mass
          if not from_unit:
              from_unit_cap = self.raw_units["charge"]
              from_unit_mass = self.raw_units["mass"]
              from_unit = from_unit_cap / from_unit_mass
  
          return from_unit / to_unit / mass