The use of a continuous delay-line synthesizer as a means for simulating transfer functions of linear systems by a very simple setting procedure is described. An analysis of the accuracy of this device as a system analogue is given, and the degree of approximation in frequency response is calculated for a number of transfer functions typical of servo systems.It is concluded that a delay-line of 26 sections will give a frequency response with not more than 5% error in the working band of frequencies for all normal servo systems.