checkCIF procedure

PLAT731

 A large ratio of the reported and calculated bond s.u.'s is found. 
 The use of a DFIX instruction might cause such a warning since 
 calculated s.u.'s are based on reported variances only.
 NOTE: s.u.'s on the unit-cell dimensions are taken into account in the   
 calculation of expected s.u.'s. This may result in large differences   
 between expected and reported s.u.'s when this contribution is not included
 in the reported s.u.'s, in particular for inaccurate unit-cells.   
 NOTE: Another source for the discrepancy between calculated and  
 reported s.u.'s can be that the validation software has access only to 
 the variances of the refined parameters as opposed to the full co-variance 
 matrix used by e.g. SHELXL for the calculation of derived parameters   
 with associated s.u.'s. Constrained/restrained refinement may cause large  
 co-variances.