This study deals with a basic system, the performance of which degenerates through random errors increasing with the square root of operating time. The probable circular error of this system can be made independent of the time by the addition to the system of supervisory equipment capable of periodic correction of the errors of the basic system. Assuming the supervisory equipment “fail safe” and subject to constant hazard type of failure, the performance of the supervised system is determined for various values of reliability of the supervisory equipment. It is shown that a great improvement in performance is possible even with unreliable supervision. Operations Research, ISSN 0030-364X, was published as Journal of the Operations Research Society of America from 1952 to 1955 under ISSN 0096-3984.