162 



PANEL DESIGN 



far enough from the control so that his 

 arm is comfortably extended at the start 

 of movement. Having both back rests and 

 foot rests contributes to the amount of pull 

 possible. The optimal conditions for push- 

 ing a hand control are about the same as for 

 pulHng, but in addition it was found that 

 maximal push was greater than maximal 

 pull and that pushing was more fatiguing 

 subjectively. Similarly in a study of tank 

 drivers, it w^as found that the greatest force 

 could be exerted on a foot pedal when it 

 was so located that the thigh made a 20 

 degree angle with the horizontal and the 

 knee angle was 165 degrees at the end of 

 the pedal stroke (18). 



More detailed information of this sort is 

 needed about the optimal positions for the 

 operation of other types of controls and for 

 the placement of displays in the best posi- 

 tions for use. In many studies, certain de- 

 sign specifications for controls and displays 

 are recommended as the best for human use, 

 but all too often, the experiments were done 

 with the controls and displays directly in 

 front of the subjects. One might ask 

 whether the design specifications hold well 

 for other locations in respect to the operator 

 or whether a different type of design would 

 be more suitable if the item were to be placed 

 in the periphery of the panel, for example. 

 At least it would be important to know in 

 what locations, other than the central ones, 

 each control and display may be used and 

 how much impairment of performance re- 

 sults from moving them different distances 

 from their optimal positions. That is to 

 say, we should have data not only on the 

 optimal position of each item on a panel, 

 but also the second and third best positions 

 in which they may be placed. 



The Importance and Frequency of Use of 

 Controls and Displays 



Methods of Investigation 



The decision to place a control or display 

 in a position other than its optimal one 

 depends primarily upon its importance and 



frequency of use. If a particular control 

 or display is crucial to the operation of a 

 piece of equipment, then it must be given 

 the highest priority and placed in a position 

 where the operator will never fail to use it 

 readily and accurately. Usually only a lim- 

 ited number of items on any panel will fall 

 into this category. For the bulk of controls 

 and displays, the frequency of use must 

 serve as the basis for deciding whether or 

 not they get placed in the preferred posi- 

 tions. Various methods have been used to 

 determine the importance and frequency of 

 use of controls and displays. As far as im- 

 portance is concerned, the only way to de- 

 termine that is to get the opinion of ex- 

 perienced operators or the engineers who 

 built the equipment, by asking them to rank 

 order or rate each control or display ac- 

 cording to how crucial it is in the operation 

 of the equipment. The same technique may 

 be used to ascertain the frequency of use of 

 controls and displays, but there are two 

 other methods which perhaps yield more 

 detailed information on this question. One 

 that may be used in studying controls is the 

 micromotion analysis technique employed 

 in industry. In this method, motion pic- 

 tures are taken of samples of the work of 

 experienced operators. By examining the 

 developed film, it is possible to count ac- 

 curately how often each control is used in 

 different types of operations. In investi- 

 gating the frequency of use of visual displays, 

 records of eye movements are of considerable 

 value, for it is possible to determine ac- 

 curately the number of fixations the opera- 

 tor makes on each display as he operates 

 his equipment. 



Essentially these methods have been used 

 in the analysis of the importance and fre- 

 quency of use of controls and displays on 

 one type of radar console (34). Here the 

 subjects were asked to rate each control and 

 display as very important, moderately im- 

 portant, or of little importance, and fre- 

 quently, occasionally, or infrequently used. 

 Then, instead of employing micromotion 



