              Residual factor R for reflections that satisfy the resolution\
               limits established by _refine_hist.d_res_high and\
               _refine_hist.d_res_low and the observation limit\
               established by _reflns.observed_criterion, and that were used\
               as the working (i.e., included in refinement) reflections when\
               refinement included calculation of a "free" R factor. Details\
               of how reflections were assigned to the working and test sets\
               are given in _reflns.R_free_details.\
\
                   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