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 reflections (i.e. were excluded from the refinement) when the refinement included the calculation of a 'free' R factor, expressed as a percentage of the number of geometrically observable reflections that satisfy the resolution limits.