checkCIF procedure

PLAT250

 An average value of the U(i,j) tensor of the asymmetric unit of a residue  
 is calculated. An ALERT is generated when the corresponding main axis U3/U1
 ratio deviates significantly from 1.0. Large values of this ratio should be
 taken as an indication of possible systematic errors in the data or errors
 in the model. Visual inspection of an ORTEP plot will show that many  
 displacement ellipsoids have their major axis pointing in the same direction.