The activity is affected by the amount of practice that one has had. It is affected by the extent to which the action has become a habit. It is affected by the degree with which one has got into the swing of the work. This may be an individual difference. Some workers find it possible to start at work at very much the pace that they will use when they are well into it. A large number of our records shows that most workers never get into the swing at the beginning of a work period. Not only the hour of the workday, but the time in the work period will have a strong effect upon the amount of work turned out. Again we have the question of spurt, when for some reason or other the activity is being performed at a pace that is above the normal pace. The effect of all these elements of the activity upon the fatigue itself depends upon the relation between mental fatigue and bodily fatigue. This relationship must be worked out by psychologists and physiologists. It is for the observer who measures fatigue in the industries to attempt to discover, as far as he can, what fatigue exists, and why it exists, and then to make both physical and mental conditions under which the activity is carried on as favorable to efficient activity as possible. Motion Study, Micromotion Study, the Cyclegraph, and the Chronocyclegraph Method as Measurers of Activity. We measure activity in two ways: 1. By motion study, which records in great detail the methods used in doing the work. 2. By records of outputs when using the various methods. [Illustration: FIG. 19 This picture shows the examination of the original micromotion films at the motion study laboratory of the New England Butt Company.] [Illustration: FIG. 19] Motion study consists of dividing the activity into the smallest units possible, measuring the variables of these units, studying the data, and deducing methods by which the activity may express itself more efficiently. Motion study, whatever its type, implies time study, in that the time the motion occupies is one test of the efficiency of the motion. Micromotion study is the name we have given to our method of recording motions and their surrounding conditions by means of a cinematograph and one of our special clocks which registers extremely small intervals of time, smaller than the elapsed time between any two pictures of the cinematograph film. The micromotion method enables us to record easily motions down to less than a ten-thousandth of a minute. This gives us all the information we could desire for purposes of time study, and the record is absolutely free from the errors in time due to the personal element. Although many of the various elements, or units, that comprise the path of a complete motion, or cycle of activity, appear on different pictures in the film, it is difficult to visualize or measure the orbit or exact path of the motions by means of the film.