code: def _handle_montage_units(montage_units, mean_radius):
      if montage_units == "auto":
          # radius should be between 0.05 and 0.11 meters
          if mean_radius < 0.25:
              montage_units = "m"
          elif mean_radius < 2.5:
              montage_units = "dm"
          elif mean_radius < 25:
              montage_units = "cm"
          else:  # mean_radius >= 25
              montage_units = "mm"
      prefix = montage_units[:-1]
      scale_units = 1 / DEFAULTS["prefixes"][prefix]
      return scale_units
  
imports: import os.path
  from os import PathLike
  from pathlib import Path
  import numpy
  from mne.utils.check import _check_option
  from ..._fiff._digitization import _ensure_fiducials_head
  from ..._fiff.constants import FIFF
  from ..._fiff.meas_info import create_info
  from ..._fiff.pick import _PICK_TYPES_KEYS
  from ..._fiff.utils import _find_channels, _read_segments_file
  from ...annotations import Annotations, read_annotations
  from ...channels import make_dig_montage
  from ...defaults import DEFAULTS
  from ...epochs import BaseEpochs
  from ...event import read_events
  from ...utils import Bunch, _check_fname, _check_head_radius, fill_doc, logger, verbose, warn
  from ..base import BaseRaw
  from ._eeglab import _readmat
label_desc: Use image node_id 8 for calling a global function with example usage: _handle_montage_units(montage_units, mean_radius) and returns: scale_units