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

  FT_CHANUNIT is a helper function that tries to determine the physical
  units of each channel. In case the type of channel is not detected, it
  will return 'unknown' for that channel.
 
  Use as
    unit = ft_chanunit(hdr)
  or as
    unit = ft_chanunit(hdr, desired)
 
  If the desired unit is not specified as second input argument, this
  function returns a Nchan*1 cell array with a string describing the
  physical units of each channel, or 'unknown' if those cannot be
  determined.
 
  If the desired unit is specified as second input argument, this function
  returns a Nchan*1 boolean vector with "true" for the channels that match
  the desired physical units and "false" for the ones that do not match.
 
  The specification of the channel units depends on the acquisition system,
  for example the neuromag306 system includes channel with the following
  units: uV, T and T/cm.
 
  See also FT_CHANTYPE