The configuration index has two digits which are the priority numbers of the ligands separated by the largest angle.
As an example, (acetonitrile)dichlorido(pyridine)platinum(II) complex where the Cl ligands may be trans or cis to one another.
The ligand priority numbers are, applying the CIP rules: In the trans case the configuration index is 1 giving the name(SP-4-1)-(acetonitrile)dichlorido(pyridine)platinum(II).
NB this procedure gives the same result as SP-4, however in this case the polyhedral symbol specifies that the complex is non-planar.
The configuration index consists of two digits which are the priority numbers of the ligands on the threefold rotation axis.
The first segment consists of two digits which are the priority numbers of the ligands on the five, six or sevenfold rotation axis.