Subjects attempting to reproduce a linear displacement response are viewed as moving until they feel that their attempted response is correct. This paper presents the argument that a quantitative predictor of their reproduction can be made in terms of the psychophysical notion of the jnd. Experiment 1 obtained an empirical estimate of the jnd for a linear displacement response. Experiment 2 was a reanalysis of the motor recognition study of Marshall (1972), from which a jnd estimate was also computed. The corresponding estimates were remarkably close and were able to predict the “recall” data from that same study.