The least-squares goodness-of-fit parameter S' for reflection
               data classified as observed (see _reflns.observed_criterion)
               after the final cycle of least-squares refinement. This
               parameter explicitly includes the restraints applied in
               the least-squares process. See also the definition of
               _refine.ls_goodness_of_fit_obs.
                    (   sum   |w    |Yobs  - Ycalc|2| )1/2
                    ( + sumr|wr |Pcalc - Ptarg|2| )
               S' = ( ------------------------------------- )
                    (      Nref + Nrestr - Nparam     )
               Yobs   = the observed coefficients
                          (see _refine.ls_structure_factor_coef)
               Ycalc  = the calculated coefficients
                          (see _refine.ls_structure_factor_coef)
               w        = the least-squares reflection weight
                          [1/(e.s.d. squared)]
               Pcalc  = the calculated restraint values
               Ptarg  = the target restraint values
               wr     = the restraint weight
               Nref   = the number of reflections used in the refinement
                          (see _refine.ls_number_reflns_obs)
               Nrestr = the number of restraints
                          (see _refine.ls_number_restraints)
               Nparam = the number of refined parameters
                          (see _refine.ls_number_parameters)
               sum  is taken over the specified reflections
               sumr is taken over the restraints