Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_determine_units”.

  FT_DETERMINE_UNITS tries to determine the units of a geometrical object by
  looking at its size and by relating this to the approximate size of the
  human head according to the following table:
    from  0.050 to   0.500 -> meter
    from  0.500 to   5.000 -> decimeter
    from  5.000 to  50.000 -> centimeter
    from 50.000 to 500.000 -> millimeter
  Use as
    dataout = ft_determine_units(datain)
  where the input obj structure can be
   - an anatomical MRI
   - an electrode or gradiometer definition
   - a volume conduction model of the head
  or most other FieldTrip structures that represent geometrical information.