Completeness (as a percentage) of symmetry-unique
               anomalous difference data within the intersection of
               (1) a spherical shell (defined by its diffraction
               limits, _reflns_shell.d_resolution_high and
               _reflns_shell.d_resolution_low) and (2) the ellipsoid
               (described by __reflns.pdbx_aniso_diffraction_limit_*
               items), relative to all possible symmetry-unique
               anomalous difference data within that intersection.