checkCIF procedure

PLAT850

 This G_ALERT can be ignored in the case that the so-called 'on-the-cheap'  
 Flack parameter is reported as determined with SHELXL. 
 Exactly zero values are possible but may also be a software artefact.  
 The following should be checked:   
 Problem #1: Some SHELXL97 versions do not allow negative values of the 
 Flack parameter when determined using the BASF/TWIN instructions.  
 Negative values are set to 0.00001. Refinement may not converge completely.
 Problem #2: Some SHELXL97 versions put meaningless values in the CIF for the   
 Flack parameter when 'TWIN -1 0 0 0 -1 0 0 0 -1 2 / BASF' instructions (i.e.   
 an explicit matrix is specified on the TWIN instruction) are used. 
 Please check the value of BASF (in the list output)  against the Flack 
 parameter in the CIF.