checkCIF procedure

PLAT152

 Some software packages calculate Volume s.u.'s incorrectly. The correct
 formula  for triclinic, monoclinic and orthorhombic systems
 (based on the propagation of error expression) may be found in:
 M. Nardelli, Computer & Chemistry, (1983), 7, 95-98.   
 or 
 C. Giacovazzo ed. in 'Fundamentals of Crystallography', Second Edition,
 Oxford University Press, 2003, p135.  
 Also note that several cell parameters for higher symmetry cells are no
 longer independent. S.u. calculations need special treatment in those cases.