In this paper the use of “circuit constants” for the calcualtion of transmission-line problems is dealt with in an elemetary way, in the hope that many who perhaps would not have the time or patience to follow the original papers of Messrs. Evans and Sels may be encouraged to use their very powerful and useful methods.To avoid having to refer to textbooks for the elements of complex algebra, a few notes on its use have been included.The formulae for calculating the constants of series and parallel circuits are developed; and the determination of the particular values of the constants for transmission lines, and for transformers, is dealt with in detail.Following this, methods for dealing with more complex cases of lines supplying more than one substation, and branching lines, are dealt with. An actual example of an existing transmission line is worked out in detail.