In order to be thoroughly satisfactory, observations of the effect of the changes upon the worker must be made during a long period. The worker’s greatest asset is his ability to work. In order to prove its value, fatigue eliminating work must actually show results in prolonging the years that he is able to devote to his life work. This in practice it does. Not only does the average worker remain physically able to work more years than where no fatigue elimination has taken place, but also through the fatigue study, and motion study, which he has co-operated to make, he learns to be able to teach that thing, or those things, at which he is most skilled, and thus to prolong his years of economic value. You must note how many of your workers are beyond the usual working age, and are still at work. Some of these will be working at the work itself; that is, in the performing department. Others will be planning or teaching the work in some way. The number of these and their condition will form an admirable unit of measurement of the success of your work. The Test of Posture. The third test is that of posture. Take another walk through your plant, and look at those workers to whom fatigue elimination work has been applied, and note how they are sitting, or standing, or walking. [Illustration: FIG. 31 A. Set of experiments in fatigue study for proving that times of motions have little close relation to lengths of motions unless the same length of motion is repeated consecutively many times. (See Fig. 21.) B. Micromotion of workman reaching with both hands for pieces of a machine which is being assembled. The microchronometer in the foreground registers divisions of time to the half a thousandth of a minute, and therefore gives us much data relating to time study, motion study, and fatigue study. C. Penetrating screen in the plane of the motions for the purpose of registering exactly the distance of motions in fatigue study experiments.] [Illustration: A B C FIG. 31] The American Posture League, with headquarters at 30 Church Street, New York City, will gladly furnish standards for proper posture in various positions. It will be impossible, of course, to eradicate wrong habits of posture in a short time, no matter how radical the change may be, but you should note improvements. At least each worker should be so placed that he could work in the proper posture if he chose, and so that the proper posture will be the easiest for him. If the chairs, benches, levers, or devices force him to assume the proper posture, so much the better. Consideration of the devices shows, unfortunately, that few are designed for operation with least fatigue; more being designed to use the least quantity of material.