Chapter 3 

 THE DESIGN AND USE OF INSTRUMENTS^ 



WILLIAM E. KAPPAUF2 



Princeton University 



Intkoduction 



Instruments are of many types and serve 

 many purposes. For each type of instru- 

 ment the problem of the design of its dis- 

 play is somewhat different, being defined in 

 terms of the way or ways in which informa- 

 tion is read or taken from the indicator and 

 in terms of the varied conditions under which 

 it will be used. 



There are, in general, two kinds of instru- 

 ment reading operation : one which proposes 

 to be accurate and obtain a quantitative, 

 numerical value from the indicator; the 

 other, a monitoring or checking type of oper- 

 ation. Readings by either form of operation 

 should conform with stated tolerances or 

 operating requirements. How well these 

 tolerances are met depends on the restrictive 

 nature of the conditions of instrument use 

 and on the adequacy with which display 

 design variables have been manipulated to 

 take particular account of the operator's 

 characteristics. 



In submarines, two considerably different 

 sets of instrument reading conditions are 

 recognized. Some instruments must be illu- 

 minated in such a way that the operator and 



' This chapter is based on portions of a review 

 prepared by the author for the Air Forces, Air 

 Materiel Command, Wright Field, Dayton, Ohio, 

 and entitled, "Studies pertaining to the design 

 and use of visual displays for aircraft instruments, 

 computers, maps, charts, and tables: A review 

 of the literature," USAF Technical Report 5765, 

 April 1949. 



2 The author is indebted to William M. Smith, 

 who, under an Air Force research contract with 

 Princeton University, assisted in the preparation 

 of the bibliography and the gathering of reference 

 material which forms the basis of this chapter. 

 (See 71.) 



his neighbors will remain as well dark- 

 adapted as possible for night observation. 

 Other instruments are used at stations 

 where operator dark-adaptation is not a con- 

 sideration and so these indicators and devices 

 may be well illuminated. Level of illumina- 

 tion is, therefore, a factor which, in any 

 thorough program of research on instrument 

 displays, must be studied in relation to all 

 other design variables. Currently available 

 data on the effects of instrument illumina- 

 tion will be presented in a special section 

 below. This will precede a discussion of 

 the design of instruments for specific read- 

 ing needs, but will follow a treatment of 

 some general matters of instrument marking 

 and numbering. 



Instrument Marking 

 Instrument-marking problems will in- 

 clude, for purposes of the present discussion, 

 all the more general aspects of the design 

 of the instrument face. In particular, these 

 are: contrast between the markings and the 

 scale face, the length and thickness of scale 

 graduation marks, the shape, size, boldness, 

 and spacing of instrument numbers, and the 

 labeling of the instrument. One does not 

 proceed very far in the experimental study 

 of these factors before discovering that they 

 involve critical interactions of the sort al- 

 ready remarked on in Chapter 2. 



Contrast between the Scale Markings 

 and the Scale Face 



When dark adaptation of the operator is 

 important, it is appropriate to use instru- 

 ments with white markings on black back- 

 grounds. Adaptation level varies, in gen- 

 eral, with the proportion of the visual field 



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