checkCIF procedure

PLAT939

 SHELXL suggests/optimizes two weight parameters aiming at bringing the S
 value (Goodness-of-Fit) close to 1.0. This 939_ALERT reports the S value when
 based on the supplied Sigma(I) values only. A large value of this not weight
 optimized S generally indicates the presence of large outliers in the data
 set. Examples are reflections (partially) 'measured' behind the beam stop.
 (See also ALERT_919). The latter low order reflections are best left out from 
 the final refinement with an OMIT hkl instruction.