              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 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.\
\
               _refine.ls_R_factor_obs should not be confused with\
               _refine.ls_R_factor_R_work; the former reports the results of a\
               refinement in which all observed reflections were used, the\
               latter a refinement in which a subset of the observed\
               reflections were excluded from refinement for the calculation\
               of a "free" R factor. However, it would be meaningful to quote\
               both values if a "free" R factor were calculated for most of\
               the refinement, but all of the observed reflections were used\
               in the final rounds of refinement; such a protocol should be\
               explained in _refine.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