checkCIF procedure

PLAT029

 Ideally (and a requirement for publication in Acta Crystallographica), 
 this fraction should be close to 1.0 for theta-full greater or equal   
 to sin(theta/lambda) = 0.6 (i.e. 25.24 degrees for MoKa and 67.7 degrees   
 for CuKa  radiation).  
 The three major causes of incomplete data sets are:
 1 - A missing cusp of data due to data collection by rotation around   
     the spindle axis only (standard on some image-plate systems).  
     Cure: collect an additional data set after remounting the crystal. 
 2 - The DENZO image processing package has problems with certain strong 
     reflections. They are often excluded from the data set.
     Cure: Add an additional scan at lower power setting in order to
     include strong low order reflections.  
 3 - Incomplete scans, possibly based on erroneously assumed higher than
     actual symmetry.   
 Note: The default value of '_diffrn_measured_fraction_theta_full' that   
 is automatically calculated and inserted in the CIF by SHELXL-97 might 
 generate A-level ALERTS when significant numbers of reflections are
 missing at higher theta values. In order to avoid such an ALERT,   
 substitute the values calculated with the SHELXL instruction 'ACTA 50' 
 for '_diffrn_reflns_theta_full' and '_diffrn_measured_fraction_theta_full' 
 respectively. For Mo-radiation, corresponding values of 25 degees (or  
 higher) and 0.99 (or higher) are expected. (See SHELXL manual).
 PLATON may be used to analyse the case at hand (by invoking either the 
 'FCF-VALIDATION' mode or the 'ASYM-VIEW' mode).