170 



PANEL DESIGN 



laj^out simultaneously. At our present stage 

 of knowledge, satisfying the requirements of 

 one principle will very likely mean violating 

 those of another. For example, if controls 

 are to be arranged in functional groups, it 

 may not be possible to place all of them in 

 positions for optimal use. Or conversely, if 

 the position of a control is fixed by the fact 

 that it requires the apphcation of maximum 

 force for operation, it may not be possible to 

 include it in a functional group that must be 

 located elsewhere on the panel. In order to 

 effect such compromises most efficiently in a 

 practical panel design problem, we should 

 have some way of assigning priorities to each 

 principle. For example, if long vigils are re- 

 quired in the operation of one type of equip- 

 ment, perhaps the position of the operator 

 should be considered first. Where speed and 

 accuracy in the use of a limited number of 

 controls is of prime importance, their loca- 

 tion should be given first priority. Or where 

 an operator has to handle a complex array of 

 controls and displays, functional grouping 

 and coding might be given first considera- 

 tion. 



Ideally any departure from the require- 

 ments of any principle should be based on 

 experimental knowledge of what alternative 

 arrangements and designs are least detri- 

 mental to performance. Since the existing 

 literature does not afford adequate data on 

 the efficiency of performance over a wide 

 range of conditions, it will be necessary, in 

 any practical situation, to proceed by em- 

 pirical trial and error and trj^ out various 

 deviations from ideal design until the most 

 satisfactorj?- arrangement is found. But it 

 should be pointed out that guesswork can 

 eventually be eliminated when we have com- 

 plete functions, describing the efficiency of 

 performance over a wide range of variations 

 in panel design. If problems this complex 

 are to be solved scientifically, it is imperative 

 that future research on human factors in 

 panel layout be carried beyond the point of 

 merely determining optimal arrangements 

 and designs. We must be able to know be- 



forehand how efficiency varies as a function 

 of different amounts of departure from the 

 optimum in any direction. 



Perhaps a more serious type of compro- 

 mise must be made between the ideal design 

 for each individual control and display and 

 the kind of design that might be called for 

 when that item is to be placed in a particular 

 context in a complex panel. It may turn 

 out to be more efficient to violate some of the 

 principles of the design of individual controls 

 and displays in order to achieve more satis- 

 factory layouts. Or the converse may be 

 the case. For example, it has been pointed 

 out that while certain control knobs or 

 handles might be optimal for best operation 

 of those controls, they may not be distinctive 

 enough to prevent confusion of one control 

 with another. The ideal would be to find 

 knob designs that are both distinctive and 

 easy to use, but in actual practice a compro- 

 mise between these two ideals may have to 

 be reached. Similarly, while it is desirable 

 to have dials and indicators some optimal 

 size, the demands of space and need for sim- 

 plicity might be so great that it would be best 

 from the operator's point of view to make 

 them suboptimal in size. Here again, it is 

 necessary to know what kinds of suboptimal 

 designs are least detrimental to overall effi- 

 ciency of operation in order to accomplish 

 such considered violations of ideals for indi- 

 vidual control and display design. For prac- 

 tical panel layout, therefore, future research 

 on control and display designs cannot stop 

 at determining just the optimal design but 

 must afford us a complete function in every 

 case, describing what varying degrees of de- 

 viation from the ideal will mean for operator 

 efficiency. 



Finally, it is necessary to make compro- 

 mises between the panel layouts that would 

 be ideal from the operator's point of view 

 and what the design engineer can do. Not 

 every rule dictated by studies of human 

 capacities can be followed in the practical 

 engineering situation. The engineer is lim- 

 ited by the structural features, mechanical 



