Abstract: Apparatus for correcting measurement errors due to cycle skipping in acoustic-wave transit time measurements.The measurement made during sequence N-1 is stored in an auxiliary memory and compared with the next measurement (sequence N). If the difference between the two successive measurements is smaller than a given fraction of the average period of the acoustic waves used, the measurement of sequence N is transmitted to a measurement memory and recorded. Otherwise, it is the last measurement considered good which is recorded. Moreover, in case of erroneous measurement, the transfer of the control signal for the gain applied to the reception signal is stopped and the gain remains at its former value.Significant improvement in the quality of acoustic well-logging recordings is achieved.