checkCIF procedure

PLAT703

 Torsion angles given in the CIF are cross-checked with corresponding values
 calculated from the coordinates.  Alerts are set at 1,2 and 3 Sigma
 deviation levels. In general, all differences should be within the associated
 s.u. Small differences may arise from rounding. Very large deviations
 normally indicate incorrectly specified symmetry operations on the associated
 atoms, or 'cut-and-pasting' of incompatible CIF's.