134 



DESIGN OF CONTROLS 



sarily exploratory and most of that which 

 was performed during wartime suffered 

 from restrictions on experimental design 

 imposed by the use of modified service equip- 

 ment and by the need to answer specific 

 questions about specific types of equipment. 



Other wartime research emphasized the 

 modification of existing equipment in the 

 direction of ease of learning, economy of 

 effort, and accuracy in using the right con- 

 trol at the right time. This research was 

 mainly stimulated by those responsible for 

 the safety and training of personnel. 



In the years preceding World War II a 

 related type of research on design and place- 

 ment of controls had been carried on by 

 industrial psychologists and time and mo- 

 tion engineers. Their major interest, how- 

 ever, was in the evaluation of motor activity 

 for specific work positions in order to elim- 

 inate waste motion and in the alteration of 

 performance in the direction of increased 

 production. 



It is well recognized that the approach 

 that is adopted for any broad research pro- 

 gram greatly affects the nature of the results 

 which are obtained. In the general lines of 

 research just discussed the approach was 

 essentially that of attempting to improve the 

 performance of certain existing man-machine 

 combinations by modification of the equip- 

 ment in current use. This approach is a 

 natural outgrowth of the history of machine 

 design. 



Traditionally, the behavior of the human 

 operator was considered unpredictable and 

 outside the realm of description in engineer- 

 ing terms. On the other hand, considerable 

 confidence was retained in the ability of the 

 operator to adapt to the requirements of the 

 operation. It became standard practice to 

 ignore operator characteristics in the design 

 of machines. The machines and their con- 

 trolling mechanisms were designed without 

 specific reference to the operator and then 

 these systems were linked to a control device 

 which, if manipulated in a certain prescribed 

 manner, would provide the desired input to 



the rest of the system. Sometimes the as- 

 sumption that the average operator could 

 and would manipulate the control device in 

 the prescribed manner was justified. More 

 often, however, it was found that the output 

 of the man-machine combination was some- 

 what less than that which was desired. 



The problems posed by the human opera- 

 tor were complicated by the apparent neces- 

 sity for using him to perform certain func- 

 tions. One approach to a solution was the 

 adoption of a general policy of reducing the 

 role of the operator to a minimum. The 

 rapid development of the engineering field 

 led to more and more success in carrying out 

 this policy. However, even in his "min- 

 imum" role the operator continued to be 

 a problem. 



Meanwhile, the observation of differences 

 in the abilities of operators and the effects of 

 practice stimulated another general attempt 

 to deal with the problems of the human 

 operator. It was found that the output of 

 the man-machine combination could be im- 

 proved and made more consistent by means 

 of selection and training of operators. This 

 attempt to "fit the man to the machine" 

 was recognized as an incomplete solution, 

 but the results were gratifying enough to 

 warrant continuance and expansion of the 

 program. 



Another method of dealing with the same 

 general problem was suggested by observa- 

 tion of the difiiculties which the operators 

 experienced with a specific piece of equip- 

 ment. It was noted that by making certain 

 obviously desirable changes in the equipment 

 the performance could be improved. The 

 success of this procedure based on casual 

 observation and trial-and-error tactics led 

 to more detailed analyses of the task, more 

 carefully controlled observation, and the 

 application of statistical checks on the 

 validity and reliability of the results ob- 

 tained from the changes which were made. 

 The investigations noted at the beginning 

 of this section are, for the most part, the 

 result of this method of approach. 



