Five years ago the performance of discrete detector sensors with which the writer had contact was specified by setting essentially an acceptable noise-equivalent target (NET), line-of-sight (LOS) accuracy, frame-time (FT), and data rate (DR). In addition, target intensity-time profiles, back-ground data, and other available information were given. Often, object detection probability, false track rate, tracking accuracy, object reporting time, and other specifications were set as well. It will be noted that the above specifications are more than a minimum complete set. Thus, there was a potential for inconsistency. More important, the mission specifications (principally object detection probability, false track rate, tracking accuracy, and object reporting time) were sometimes missed even though NET and FT values were met because the object-intensity and the background models used to connect them with NET, LOS accuracy, and FT were inaccurate. The sensor (or its subsys-tems) was either overspecified, making it overly expensive, or it was underspecified, making it in-capable of performing its mission adequately. No criticism is intended for the workers who made specifications for previous programs. They did the best they could with the information they had available. However, it was clear at that time that a better procedure was needed if optimum system performance was to be achieved for minimum cost.