An expression is derived from which, by substitution of appropriate numerical values, an equation can be obtained for any of the intermodulation products which can be generated by the simultaneous transmission of any number of sinusoidal waves through a device with an output/input characteristic likeV=a1v+a2v2+a3v3…. This expression is used as a basis for classification of products, and a table of representative products is drawn up. Information is given about the numbers and relative importance of products of different kinds.