STUDIES OF HUMAN FACTOR IN PANEL DESIGN 



161 



are no experimental data to indicate whether 

 such arrangements can be practically em- 

 ployed in equipment design. It may be 

 that, as equipment gets more complex and 

 more space for controls and displays are 

 needed, several panels placed around a single 

 operator, or two operators working as a 

 team, will have to be used. This is the 

 practice in many current types of aircraft. 

 But whether it is the best arrangement for 

 all types of situations, only direct experi- 

 mental attack on the problem will tell. 



Optimal Location of Controls 

 and Displays 



Within the practical Umits of the working 

 area, controls and displays should be placed 

 in optimal positions for use by the operator. 

 The basic questions to be asked here are: 

 What positions on the panel are best for the 

 use of different types of controls and 

 displays? Where should a control best be 

 placed which demands strength, speed, or 

 precision in operation? What should be the 

 position of displays that have to be read 

 accurately and those that require only a 

 cursory check? In general, it is pointed 

 out by Bartlett that the best position for 

 most hand operated controls is directly in 

 front of the operator between shoulder and 

 waist height (3, 4). Similarly it may be 

 said that displays placed at eye height, in 

 front of the operator will be seen most ac- 

 curately and with least effort. In fact, one 

 study of the placement of alternative dis- 

 plays in this position on the instrument panel 

 showed that pilots tended to fixate the dis- 

 plays in the central area the largest number 

 of times regardless of whether they indicated 

 horizon, direction, or turn and bank in flight 

 (20). Of course, one might well expect that 

 other positions on the panel will serve as 

 well or better than these central ones for 

 the use of certain controls and displays. 



Localization of Controls 



As far as simply reaching accurately for 

 controls is concerned, Fitts has shown that 



performance is best when they are located 

 at shoulder height in front of the operator 

 (12). He studied the ability of 50 pilots 

 to localize targets placed around them in a 

 cockpit mock-up . The subj ects had to fixate 

 a red bulb through slits in opaque goggles, 

 thereby fixing the head in simulation of 

 certain flight conditions. Then, in response 

 to instructions they tried to locate the center 

 of each target by marking it with a small 

 stylus held in either the left or the right 

 hand. When required to reach for targets 

 above shoulder level, it was found that they 

 tended to aim too low, and with targets 

 below shoulder level, too high. Errors in 

 localization increased with targets placed 

 on either side of the operators and became 

 largest with the targets located farthest to 

 the rear. 



Placement of Controls 



Very few experiments have been done to 

 carry the problem of the placement of con- 

 trols beyond studying the accuracy of reach- 

 ing for them. There is one investigation 

 of the efiiciency of turning handwheels as 

 a function of their location on a 47^ by 47^ 

 inch vertical surface (35). It showed that 

 there were Umited areas within which wheels 

 of 1^ inch diameter could be operated most 

 efficiently by each hand. For 11 seated 

 subjects, the best region for each hand was 

 an irregularly shaped area on the panel, 

 about 16 by 20 inches, with its center about 

 12 inches below the horizontal hne of sight 

 and 20 inches to the left and right of the 

 midline of the body for the left and right 

 hands, respectively. The maximal areas 

 within which the handwheels could be opera- 

 ted with 80% efficiency by each hand were 

 more than twice the size of the optimal 

 areas and were well within the limits of 

 reach of the particular subjects used. Some 

 information is available on the placement 

 of hand controls for the maximum amount 

 of pull and push (19). In general, pull is 

 maximal when the hand grip is at about 

 elbow height, and the subject has his seat 



