ZEROCOMBINE:

        input = "*bias*.imh"    List of zero level images to combine
      (output = "Zero")         Output zero level name
     (combine = "average")      Type of combine operation
      (reject = "sigclip")      Type of rejection
     (ccdtype = "")             CCD image type to combine
     (process = no)             Process images before combining?
      (delete = no)             Delete input images after combining?
     (clobber = no)             Clobber existing output image?
       (scale = "none")         Image scaling
     (statsec = "")             Image section for computing statistics
        (nlow = 1)              minmax: Number of low pixels to reject
       (nhigh = 1)              minmax: Number of high pixels to reject
       (nkeep = 1)              Minimum to keep (pos) or maximum to reject (neg
       (mclip = yes)            Use median in sigma clipping algorithms?
      (lsigma = 2.5)            Lower sigma clipping factor
      (hsigma = 2.5)            Upper sigma clipping factor
     (rdnoise = "0")            ccdclip: CCD readout noise (electrons)
        (gain = "0")            ccdclip: CCD gain (electrons/DN)
      (snoise = "0.")           ccdclip: Sensitivity noise (fraction)
       (pclip = -0.5)           pclip: Percentile clipping parameter
       (blank = 0.)             Value if there are no pixels
        (mode = "ql")