              Residual factor R for reflections that satisfy the resolution\
               limits established by _refine.ls_d_res_high and\
               _refine.ls_d_res_low and the observation limit established by\
               _reflns.observed_criterion, and that were used as the test\
               (i.e., excluded from 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