A circuit is given by means of which a calculator for screened linear radium sources, described in a previous paper, can be used for investigating the combined dosage due to a small number of sources in tandem when the line densities of the constituent sources differ. An example of the application of this circuit to the problem of the treatment of cylindrical surfaces by axial sources is given, showing that the apparatus developed makes it possible to consider in detail the dosage distribution in individual cases in a manner not hitherto considered practicable. A number of other applications are also indicated.