checkCIF procedure

PLAT026

 Check whether a sufficient %fraction of the symmetry averaged unique 
 reflection set (= '_reflns_number_total') is indeed above the noise level
 (= '_reflns_threshold_expression') as measured by the ratio:
       100 * ('_reflns_number_observed' or '_reflns_number_gt')
       -------------------------------------------------------- 
                  ('_reflns_number_total') 
 Check whether this low %ratio is caused by weak data beyond the recommended 
 minimum sin(theta)/lambda = 0.5 Ang**-1 resolution. Consider removal higher 
 resolution shells beyond 0.5 Ang**-1 from the refinement when clearly noise.
 A ratio below 0.5 in all resolution shells (in particular the lowest 
 resolution shells) may also point to missed translation symmetry such as 
 unit-cell halving. Similarly, (missed) twinning might result in a low %. See
 the resolution shell statistics in Section 6 of the validation '.ckf' file.