checkCIF procedure

PLAT033

 Check the relevance/validity of the absolute structure determination. Please
 refer to Flack,H.D. & Bernardinelli, G. (1999) Acta Cryst. A55, 908-915 and
 (2000) J. Appl. Cryst., 33, 1143-1148. A value of the Flack parameter that
 deviates significantly from zero  (taking into account the associated s.u.)
 might indicate that the absolute structure should be inverted in case of a
 value closer to 1.0 than to zero. A value close to 0.5 may be indicative of
 an inversion twin or a missed centre of inversion. For valid absolute
 structure assignments, abs(x) should be less than 2 * s.u., with s.u. < 0.04.
 For enantiopure compounds, s.u. should be less than 0.1.