Core dictionary (coreCIF) version 2.4.5
Fraction of crystal point-group unique reflections (i.e. symmetry-independent in the crystal point group) measured out to the resolution given in _diffrn_reflns_resolution_full or _diffrn_reflns_theta_full. For space groups that do not contain a centre of symmetry the reflections h,k,l and -h,-k,-l are independent. This number should not be less than 0.95, since it represents the fraction of reflections measured in the part of the diffraction pattern that is essentially complete.
The permitted range is 0.95 -> 1.0
Related item: _diffrn_measured_fraction_theta_full (alternate)