In recent years tnare has been increasing interexts incorrelation functions in such fields as automalic control and communication. One of the reason for this is that the autocorrelation function provides a statistical means for optimum setting when the input to a control system is an stationary random process. A simple digital device is described for computing the autocorrelation function and spectral density which is its Fourier tratnsform. The input function to be correlated are fed intothe

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... rrelator by a pair of punched tape. Provision ismade for varying the delay of theprocession of one tape with respect to the other. The correlator Consists of tape reader, selector and amplifier circuit, solenoid motor, ten keo electric desk calculaing-machine controlled by a set of programming switch.