the wave form in fig5 it is noted that here with the frequency of the input signal of the source 10 cycles per second the frequency of the signal produced at the output terminal ot is 10 5 cycles per second thus in either case that is whether the frequency of the source is to be increased or decreased in each second the input signal is delayed in time in the delay line a number of cycles equal to the frequency error and the output taps of the delay line are successively coupled to the output terminal ot at a rate n t such that the rate of change of the taps n t times the portion of the cycles delayed in the delay line u03b4t s t s is equal to the number of cycles in the frequency error f e as noted above while an example has been used showing operation of the apparatus in correcting a frequency of 0 5 hz out of 10 0 hz the apparatus would typically be used to correct for errors of up to several hundred hz out of several mh in this more typical operation rather than fed to source signal having frequency f s directly to the enable terminal en of register 30 as shown in fig1 the source signal would fed into a frequency divider the frequency divider would provide a signal having a frequency f s m where m is an integer and would then feed the enable terminal en of the register 30 thus the enable terminal en would.