PLAT024

 Averaging of Friedel pairs is strongly advised when indicated by a
 large su on the Flack parameter. Large su values indicate that the
 anomalous scattering power is too small in combination with the data
 quality at hand to merit refinement with a non-averaged dataset. This
 will generally be the case with MoKa datasets for structures containing
 atoms not heavier than Si. The value of the Flack parameter will be 
 largely meaningless anyway for large su values. 
 
 Use MERG 3 or MERG 4 in case of refinement with the SHELXL97 program.
 Non-compliance with the above for valid scientific reasons should be
 discussed in detail in the experimental section of the paper.