15. The Economy Of Movement
The practical aspect of labor is inseparable from the study of the human being, with close attention to its functions and capacities. For instance, those who study industrial efficiency are inexorably drawn to the issue of fatigue, as any process must accommodate the limits of human endurance in order to be possible to execute, and must stay well within those limits to be practicable for long hours each day. To prescribe any activity that exceeds those limits is pointless, and will never be possible to put into practice.
In this regard, scientific managers have had some success by eliminating superfluous movements and training workers to the most effective and efficient processes, with all due consideration for the function and capacity of the human machine. In Gilbreth's study of masons, he considered every motion necessary to move a brick from the yard to its final position in the wall, considering that this would not be done once but thousands of times in the course of construction, and defined the manner in which the bricks could be carried with the least possible effort.
It's also mentioned in passing that the study of motion should also be attentive to non-motion, particular the moments in which motion is suddenly stopped, because it takes an effort to counteract the momentum. For example a person carrying a load of bricks is at the greatest risk for strain or injury if he must come to a sudden stop, such that a process of smooth motions requires less effort than one in which motions are jerky. Momentum must be considered and motions designed for fluidity from start to finish.
The primary method by which work gains efficiency is in the reduction of unnecessary motions. In this regard Gilbreth was "a virtuoso" who could observe any activity and quickly recognize movements that were excessive or entirely unnecessary, and by eliminating them increase the speed of work while reducing the exertion of the worker.
Men generally find the way to a practicable process on their own: without any instruction, a beginner will do the work as best he can, recognize tasks that are taxing, and recognize by increments a more efficient process. But while simple practice can discover some efficiencies, it generally ends at a process that is "simple enough while effective" rather than one that is as simple and as effective as possible. This requires careful observation and thorough consideration.
Thus, only in a laboratory setting can an investigator discover each motion in a process and study with exactitude the manner in which they rely upon the functions and capacities of human physiology and psychology, though the latter is set aside for the present chapter.
Once the most efficient process has been designed, it must be implemented: men must be trained to follow the process and mistakes must be observed - but it must be recognized that a mistake may not be the failure of the worker to comply with the process, but of the design failure of a process that is poorly designed to the capabilities of the worker.
Where the mistake be the failure of the worker, this is often due in part to an inability to perceive or remember the movement. It may also be in the inability to apply the movement to the context of an actual activity. It may be fatigue of the mind or the body.
It is noted that when a movement is done repetitively, the precision of the movement first seems to increase, then rapidly decrease as boredom and fatigue take their toll on the worker's ability to give adequate focus and attention to his actions. This supports the connection between the level of exertion and monotony and efficiency.
In effect, the most accurate and efficient action that can possibly be performed is not the most accurate and efficient action that can be performed over a long period of time. That is, the method of lifting a brick that requires two seconds may impart a level of fatigue, such that two-seconds-per-brick is not a rate at which work can be sustained. Meanwhile, a separate method that requires three seconds may enable the worker to sustain that rate of performance for several hours.
(EN: This is one of the defects of scientific management, in that it is assumed that the speed of an action in a laboratory will be the same speed as it will be done in the field. But in the laboratory, the subject must perform the action only a few times while being well rested, and experiments seldom are conducted to examine efficiency and accuracy over an eight- to ten-hour period, five days in a row, such as they will be performed in a real working situation. My sense is that this can be remedied by field observations or real performance measurements, and that such audits are seldom done because of the time required.)
Aside of fatigue, there is also the question of rapidity of movement: it may be anatomically possible for a motion to require half a second, but when it is done repeatedly over minutes and hours, the rate decreases, due not only to fatigue but also the effort required to stop the motion and reset the body to its original position.
There is also the matter of accuracy: to move at random requires little control or attention, and it seems that in some instances large motions require less time than more minute ones. For example, Munsterberg's laboratory experiment found that moving a hand 14 centimeters could be done with accuracy at a rate of 120 times per moment, but a motion of only one centimeter could be done with accuracy at a rate of 40 repetitions per minute.
(EN: I recall a reproduction of his experiment that required participants to touch two buttons with their forefinger, at various distances apart. His results were confirmed - but also augmented by studying the difference between hands [a right-handed person was much slower and clumsier with his left], using thumbs instead of fingers, and placing the buttons on the floor to test the speed and accuracy of feet on pedals. Interesting stuff - and it occurs to me that there must someplace be tables that could be consulted in designing tasks.)
Munsterberg admits that his studies in human motion have been very precise and exacting - and that he has no expectation that managers of industrial concerns will be quite as persnickety as laboratory investigators. But it is likely sufficient that they consider these principles in a general manner, borrowing what they can of the findings and methods of investigations when they measure and design real-world activities.