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