average

 AVERAGE N1 N2 N3 METHOD WEIGHTS -- Averages spectra together

 Parameters: 
     
  N1    -- Slot number of first spectrum to average
  N2    -- Slot number of last spectrum to average
  N3    -- Slot in which to put results
  METHOD - Averaging method. At present supports
           U  -- Unit weights
           D  -- Dwell weights
           R  -- Response weights
           V  -- Variance weights

  WEIGHTS -- a file of weights that multiply whatever weights are generated
             by method. <CR> to ignore. The weights should be for every
             spectrum regardless of selection.

 Response weights are proportional to the local ratio of COUNTS/FLUX
 and thus effectively add the counts together (optimum for photon
 counting data). Variance weights use a single value equal to the
 mean Signal/noise**2 for each spectrum.

 Average is the command to use if you are combining spectra covering different
 wavelength ranges of the same object. If these overlap at all response 
 weights are designed to optimise the signal-to-noise on a pixel by pixel 
 basis. This is useful when as is typical in the overlap region one or other
 spectrum is better than the other and which is better changes with the
 exact wavelength.

 Selection is done. 

 The spectra must have equal numbers of pixels, but no other properties
 in common. A warning is given if the wavelength scales differ but
 averaging still goes ahead

This command belongs to the classes: arithematic and manipulation .