checkCIF procedure

PLAT918

 This ALERT reports on the number of reflections with   
 (F(obs)**2 - F(calc)**2) / Sigma(F(obs)**2) < - 100.0. In case of strong
 reflections this might be due to extinction (to be addressed with the
 refinement of an extinction parameter. Otherwise those reflections are better
 removed from the final refinement since they are in systematic error. Of
 course, a valid reason for this problem should be found.