              The number of 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.