Gets channel unit.

        Channel can be specified in two ways:

        * using the first positional argument *name*

            * if there are multiple occurrences for this channel then the
              *group* and *index* arguments can be used to select a specific
              group.
            * if there are multiple occurrences for this channel and either the
              *group* or *index* arguments is None then a warning is issued

        * using the group number (keyword argument *group*) and the channel
          number (keyword argument *index*). Use *info* method for group and
          channel numbers


        If the *raster* keyword argument is not *None* the output is
        interpolated accordingly.

        Parameters
        ----------
        name : string
            name of channel
        group : int
            0-based group index
        index : int
            0-based channel index

        Returns
        -------
        unit : str
            found channel unit

def get_channel_unit(self, name=None, group=None, index=None):
        """Gets channel unit.

        Channel can be specified in two ways:

        * using the first positional argument *name*

            * if there are multiple occurrences for this channel then the
              *group* and *index* arguments can be used to select a specific
              group.
            * if there are multiple occurrences for this channel and either the
              *group* or *index* arguments is None then a warning is issued

        * using the group number (keyword argument *group*) and the channel
          number (keyword argument *index*). Use *info* method for group and
          channel numbers


        If the *raster* keyword argument is not *None* the output is
        interpolated accordingly.

        Parameters
        ----------
        name : string
            name of channel
        group : int
            0-based group index
        index : int
            0-based channel index

        Returns
        -------
        unit : str
            found channel unit

        """
        gp_nr, ch_nr = self._validate_channel_selection(name, group, index)

        grp = self.groups[gp_nr]

        channel = grp.channels[ch_nr]

        conversion = channel.conversion

        unit = conversion and conversion.unit or channel.unit or ""

        return unit