              Residual factor R for reflections that satisfy the resolution\
               limits established by _refine_ls_shell.d_res_high and\
               _refine_ls_shell.d_res_low and the observation criterion\
               established by _reflns.observed_criterion.\
\
                   sum|F~obs~ - F~calc~|\
               R = ---------------------\
                        sum|F~obs~|\
\
               F~obs~  = the observed structure factor amplitudes\
               F~calc~ = the calculated structure factor amplitudes\
\
               sum is taken over the specified reflections