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

  FT_REALTIME_HEADLOCALIZER is a realtime application for online visualization of the
  head position indicator (HPI) coils in CTF275 and Elekta/Neuromag systems.
  Repositioning within a recording session can be achieved by marking the HPI
  coil positions at an arbitrary point, i.e. by clicking the 'Update' button.
  Black unfilled markers should appear which indicate the positions of the coils
  at the moment of buttonpress. Distance to these marked positions then
  become colorcoded, i.e. green, orange, or red.
  Repositioning between a recording session, i.e. to a previous recording session,
  can be achieved by specifying a template; e.g. by pointing to another dataset;
  e.g. cfg.template = 'subject01xxx.ds' (CTF only), or by pointing to a textfile
  created during a previous recording; e.g. cfg.template = '29-Apr-2013-xxx.txt'.
  The latter textfile is created automatically with each 'Update' buttonpress.
  Use as
  with the following configuration options
    cfg.dataset         = string, name or location of a dataset/buffer (default = 'buffer://odin:1972')
    cfg.template        = string, name of a template dataset for between-session repositioning (default = [])
    cfg.bufferdata      = whether to start on the 'first or 'last' data that is available (default = 'last')
    cfg.coilfreq        = single number in Hz or list of numbers (Neuromag default = [293, 307, 314, 321, 328])
    cfg.blocksize       = number, size of the blocks/chuncks that are processed (default = 1 second)
    cfg.accuracy_green  = distance from fiducial coordinate; green when within limits (default = 0.15 cm)
    cfg.accuracy_orange = orange when within limits, red when out (default = 0.3 cm)
  This method is described in Stolk A, Todorovic A, Schoffelen JM, Oostenveld R.
  "Online and offline tools for head movement compensation in MEG." 
  Neuroimage. 2013 Mar;68:39-48. doi: 10.1016/j.neuroimage.2012.11.047.