docs: def flatcombine(arrays, masks=None, dtype=None, scales=None,
                  low=3.0, high=3.0, blank=1.0):
      """Combine flat arrays.
  
      :param arrays: a list of arrays
      :param masks: a list of mask arrays, True values are masked
      :param dtype: data type of the output
      :param out: optional output, with one more axis than the input arrays
      :param blank: non-positive values are substituted by this on output
      :return: mean, variance of the mean and number of points stored
      """
  
      result = sigmaclip(arrays, masks=masks,
                         dtype=dtype, scales=scales,
                         low=low, high=high)
  
      # Substitute values <= 0 by blank
      mm = result[0] <= 0
      result[0, mm] = blank
      # Add values to mask
      result[1:2, mm] = 0
  
      return result