Accuracy of the structural parameters determined by the least-squares refinements and the features of residual electron densities are affected by the errors both in the observed and calculated X-ray structure factors, as well as by the refinement procedures. These errors are summarized and discussed. Anomalous dispersion effect could be one of these error sources if it is not treated properly. Some successful examples are given, in which the absolute configuration of molecules composed of light atoms is determined by means of X-ray anomalous scattering.
