STUDIES OF HUMAN FACTOR IN PANEL DESIGN 



159 



The Position of the Operator 



The spatial limits within which the opera- 

 tor can work his equipment depend a great 

 deal upon the position which he assumes 

 in front of the panel. In determining the 

 limits of reach and vision in the above ex- 

 periments, the position of the subject's body 

 was always fixed, his shoulders and hips in 

 the case of hand and foot reaching and his 

 eyes in the case of vision. Any deviation 

 from these fixed positions, of course, throws 

 all determinations off by some constant 

 amount and might, for example, put some 

 controls out of his reach. With proper panel 

 design, the operator should be able to get 

 into a position to reach all controls by plac- 

 ing himself at a suitable distance from some 

 standard control and display reference 

 points. Since a man has to be comfortably 

 seated for long periods of time in many 

 types of equipment, however, he should be 

 able to move his seat with him as he has 

 to change his position. One investigation, 

 relevant to this problem, is a study of the 

 proper seating of 52 subjects who cor- 

 responded in body size to the 3000 aviation 

 cadets measured in the anthropological 

 studies (29). While the study was rather 

 specific to cockpit problems, it is of some 

 value to discuss it here, for it represents a 

 good model of the kind of work that has 

 to be done in connection with all seating 

 problems. Each subject was allowed to 

 make his own seat adjustment in a cockpit 

 mock-up, and then measurements of the dis- 

 tances to the various parts of the cockpit 

 mock-up were made. Several recommenda- 

 tions were made on the basis of the results 

 that were found. First, since the range of 

 distances from the reference point of the 

 seat to the rudder pedal was 35.5 to 41.5 

 inches (mean 39.1 inches), it was concluded 

 that cockpit seats should have six-inch fore 

 and aft adjustment that can be made in 

 one-inch increments. Second, the range of 

 seat to eye heights was 28.1 to 35.1 inches 

 (mean, 31.8 inches) with the chair at 90 

 degrees; with the chair at 103.5 degrees, 



the range was reduced to 26.9 to 34.0 inches; 

 natural slumping lost another 0.3 to 2.6 

 inches in seat to eye height. In any case, 

 it seems desirable to have the height of 

 the seat sufficiently adjustable to be certain 

 that most operators will be able to get into 

 the optimal position and still be comfortable. 



Seating Comfort. In addition to the 

 problem of positioning operators so they 

 can reach controls, some details have been 

 worked out on what constitutes the most 

 comfortable seating arrangement in the cock- 

 pit type of seat. In one study, the angle 

 of flexion of the arms and legs positioned 

 on the rudder and stick were varied by 

 adjusting the distance of the seat from these 

 controls (17). No difference was found in 

 the performance of a pursuit task when 

 angles of 105, 120, and 135 degrees were 

 used for either the arms or legs. But a 

 survey of the opinion of the subjects showed 

 that a 120 degree angle of the leg and 105 

 and 120 degree angles of the arms were 

 judged the most comfortable. Within cer- 

 tain practical hmits, then, it appears that 

 the operator can select the most comfortable 

 working position without a decrement in 

 his performance. Under some circumstan- 

 ces, however, individual adjustment is ap- 

 parently not desirable. When 20 pilots were 

 allowed to choose their own seating arrange- 

 ments in a standard cockpit, it was found 

 that they could sit comfortably for an aver- 

 age time of four hours and nineteen min- 

 utes (30). Then, when 21 other pilots were 

 required to sit in the average seating ar- 

 rangement used in the first experiment, it 

 turned out that they could sit comfortably 

 for an average of seven hours. x'Vpparently, 

 there are certain limitations in the choice of 

 individual pilots, so that it is better to de- 

 termine experimentally the most comfortable 

 seat for long sessions of operation than to 

 have operators choose their own. 



Other Seating Problems. More complete 

 data are needed on the role of seating in the 

 efficiency of operating panels before we can 

 know which arrangements are the most com- 



