Residual factor for the reflections (with number given by
               _reflns.number_gt) judged significantly intense (i.e. satisfying
               the threshold specified by _reflns.threshold_expression)
               and included in the refinement. The reflections also satisfy
               the resolution limits established by _refine.ls_d_res_high and
               _refine.ls_d_res_low. This is the conventional R
               factor. See also _refine.ls_wR_factor_ definitions.
                   sum | F(obs) - F(calc) |
               R = ------------------------
                         sum | F(obs) |
               F(obs)  = the observed structure-factor amplitudes
               F(calc) = the calculated structure-factor amplitudes
               and the sum is taken over the specified reflections