code: def _check_orig_units(orig_units):
      """Check original units from a raw file.
  
      Units that are close to a valid_unit but not equal can be remapped to fit
      into the valid_units. All other units that are not valid will be replaced
      with "n/a".
  
      Parameters
      ----------
      orig_units : dict
          Dictionary mapping channel names to their units as specified in
          the header file. Example: {'FC1': 'nV'}
  
      Returns
      -------
      orig_units_remapped : dict
          Dictionary mapping channel names to their VALID units as specified in
          the header file. Invalid units are now labeled "n/a".
          Example: {'FC1': 'nV', 'Hfp3erz': 'n/a'}
      """
      if orig_units is None:
          return
      valid_units = _get_valid_units()
      valid_units_lowered = [unit.lower() for unit in valid_units]
      orig_units_remapped = dict(orig_units)
      for ch_name, unit in orig_units.items():
          # Be lenient: we ignore case for now.
          if unit.lower() in valid_units_lowered:
              continue
  
          # Common "invalid units" can be remapped to their valid equivalent
          remap_dict = dict()
          remap_dict["uv"] = "µV"
          remap_dict[
              "μv"
          ] = "µV"  # greek letter mu vs micro sign. use micro
          remap_dict["\x83\xeav"] = "µV"  # for shift-jis mu, use micro
          if unit.lower() in remap_dict:
              orig_units_remapped[ch_name] = remap_dict[unit.lower()]
              continue
  
          # Some units cannot be saved, they are invalid: assign "n/a"
          orig_units_remapped[ch_name] = "n/a"
  
      return orig_units_remapped
  
file_path: mne-python/mne/_fiff/utils.py
imports: import os
  import os.path
  import numpy
  from .constants import FIFF
  from .meas_info import _get_valid_units
label_desc: Use image node_id 1 for calling a global function with example usage: _check_orig_units(orig_units) and returns: orig_units_remapped