The paper presents a comparison of Millington's method and the equivalent numerical distance method with theory. It is shown that Millington's method may be used in most practical problems of groundwave propagation. For overland paths the errors of this method are very small; for land-sea paths they may be larger, up to about 2.7 dB for 2-section paths, up to about 5.5 dB for 3-section paths, and up to about 2.5 dB for each land-sea boundary for very long paths. In most cases the equivalent numerical distance method shows considerable errors. This method may be used for paths representing small numerical distances, especially for overland paths. It may also be applied to longer paths when the differences between the electrical parameters of the sections are insignificant.