checkCIF procedure

PLAT032

 Check the validity of the absolute structure determination.
 A high s.u. indicates that the experimental data do not support the
 determination of the absolute structure. This will generally be the case   
 with light atom MoKa data where f" is nearly zero. 
 Note: Use the TWIN & BASF 0.0 instructions in SHELXL97. The default
 FLACK parameter is not always reliable, in particular when strongly
 correlated with the position of the origin (e.g. along y in space-group P21).  
 Please refer to Flack,H.D. & Bernardinelli, G. (1999) Acta Cryst. A55, 
 908-915 and (2000) J. Appl. Cryst., 33, 1143-1148.