Remarks on the interpretation of very high-precision measurements of hyperfine-structure splittings in neutral and singly ionized complex atoms

The studies of hyperfine structure (HFS) of flee atoms is shortly summarized. A hyperfine structure many-body parametrization method is described. The utility of this method as a source of information on atomic structure and for prediction of hfs of the fine structure levels, still undetermined experimentally, has been demonstrated on the examples of Co, Ti and Ta atoms.