158 



PANEL DESIGN 



new types of equipment. Wherever pos- 

 sible, old equipment should be revised to 

 meet the requirements set by the limits of 

 reach of the population using it. At the 

 present time, however, there is still no 

 answer to the question of how detrimental 

 to performance stretching to reach controls 

 may be. In some equipment, overcrowding 

 of panels makes it impractical to place all 

 controls within easy reach of the operator. 

 It would be valuable to know, therefore, 

 what amount and what kind of stretching 



TABLE II 



A Comparison of the Distance (in Inches) 



Required to Reach Areas of the R5D 



Cockpit with the Maximum Reaches 



Possible for 50% of King's Navy 



Population 



(From Channell, 7) 



* See Fig. 10 for diagram of cockpit areas. 



can be tolerated without introducing enough 

 fatigue or strain to impair normally required 

 performance. Of course, a great deal will 

 depend upon the nature of operation and 

 frequency of use of the controls which the 

 operator might have to strain to reach. 



The Practical Working Area for Displays. 

 The limits within which visual displays may 

 be placed in the working area are a less 

 clearly defined problem than the one faced 

 in the case of controls. A great deal depends 

 upon the general illumination which can be 

 tolerated on the panel, the size, shape, and 

 detailed design of the displays, and other 

 demands which are made on the eyes of the 

 operator. As in the case of controls, it has 

 been a matter of general belief that fatigue 



is least and performance best when there are 

 a minimum of eye and head movements 

 required in the viewing of displa3^s. Under 

 the most extreme conditions of head and 

 eye movement, with the body fixed in posi- 

 tion, the average operator can fixate his 

 eyes from 90 degrees above the horizontal 

 to about 90 degrees below; and at least 90 

 degrees to either side (31). With unlimited 

 head and body movement allowed, of course, 

 vision in almost any angle around the opera- 

 tor can be achieved. In the other extreme, 

 where the head is held in position and the 

 eyes are fixated on a point in front of the 

 observer, only a relatively small area around 

 the point of fixation is in clear focus. For 

 one eye, vision at five degrees from the 

 fovea is only about one half as good as 

 central vision (9). The value is higher for 

 the two eyes together, but in any practical 

 case depends upon the size of the objects 

 to be seen, the distance from the eyes, gen- 

 eral illumination, etc. In actual practice, 

 of course, maintenance of steady fixation is 

 rare; both the eyeballs and head rotate in 

 the process of fixating objects out in the 

 periphery. There are two basic problems 

 in determining the practical limits of vision, 

 then: (1) How much do the fatigue and 

 time involved in making head and eye move- 

 ments impair performance? (2) At what 

 distances and angles around an observer 

 may displays be placed without impairment 

 of good detailed vision? As far as this sec- 

 ond point is concerned, it is obvious that a 

 display that is placed far out laterally on a 

 vertical surface cannot be viewed squarely 

 and therefore cannot be read accurately. 

 But we have no data at present to tell us 

 how far laterally a display may be placed 

 on vertical, or any other type of surface and 

 still be seen clearly enough to be used. Be- 

 fore we can be specific about the practical 

 limits of vision on display panels, answers 

 to both of these questions must be worked 

 out experimentally. Until that time, com- 

 mon sense, hit-or-miss methods are the only 

 ones at our disposal. 



