Add to ORKGIn this paper the improved surface charge model discussed in parts I and II is used to calculate the magnetic field of a combination of materials. This new model assumes a position dependency instead of a constant surface charge. The structure under consideration consists of a magnet (µr = 1.05) and a smaller soft-magnetic material (µr = 700) on top of that. The results show that 4 or 5 iterations are necessary to accurately calculate this structure, which is similar to the number of part II