Autocorrelation function of a 4-level m sequence

In a recent communication, Balza, Fromageot and Maniere described how to generate 4-level maximum-length sequences, and listed several of the properties of these sequences. Some of the expressions for the autocorrelation function are incorrect, and it is the purpose of this letter to give the correct formulas, and to show how to reduce the off-peak autocorrelation by choosing different analogue levels to correspond with the levels of the sequence.