checkCIF procedure

PLAT090

 The data/parameter ratio of a quality structure determination in a
 non-centrosymmetric space-group containing atoms with Z greater than 18 is
 expected to be higher than 8. This ratio can be improved by refining
 Hydrogen atoms bonded to Carbon riding on their carrier atom. The number
 of reflections used in this ratio is that of the Laue averaged set. The
 validation test criteria used are expected to be met with a dataset complete
 with a resolution sin(theta)/lambda >= 0.6 Ang-1. 
 Hydrogen atom parameters are often meaningfully refined with OLEX2/NoSphereA2
 non-spherical scattering factors. In that case a G-Alert is issued with data
 resolution >= 0.6 Ang-1 and data/parameter ratio > 5 and <= 8.