DESIGN AND USE OF INSTRUMENTS 



within the size Hmits studied. Thus, the 

 data in Fig. 8 are plotted in terms of unit 

 scale length in degrees. Note that the aver- 

 age reading times of these accuracy mo- 

 tivated subjects ranged from about two to 

 five seconds. 



Schemes of Varying or Accenting Gradu- 

 tion Marks. To make the graduation 



the wrong direction, occur frequently. 

 Christensen's scheme, called staircase scal- 

 ing, involves the use of progressively longer 

 marks to designate each of the un-numbered 

 graduations within a larger division. Mark 

 length thus becomes a symbol for the numer- 

 ical value represented by the mark. Sample 

 scales in this form are shown in Fig. 9. In 



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Fig. 8. Average time per reading for dials graduated by tens and hy fives. Data from Kappauf and 

 Smith (41) for six subjects, each of whom made 30 readings for each type and size of dial under instruc- 

 tions to be as accurate as possible. Brightness level: six foot lamberts. 



scheme easy to interpret, main division 

 marks are sometimes lengthened, made 

 bolder, marked with characteristic symbols 

 or left incomplete or shorter than other 

 marks at the scale circumference, so that the 

 scale appears to have a break in it. 



Maier (58), in the course of comparing 

 reading accuracy for several commercially 

 available stopwatch faces, tested some scales 

 with and some scales without the "break" 

 just referred to. His conclusion was that 

 for scales which are to be read to the nearest 

 mark, the scale break is undesirable. 



Christensen (16) recently proposed a 

 method of varying graduation mark length 

 which may prove useful on special scales 

 where readings are ambiguous or where 

 errors of reversal, i.e., reading the scale in 



Fig. 9. Examples of the staircase scale. 

 Christensen (17) 



From 



a preliminary test of reading performance on 

 staircase scales and on conventionally gradu- 

 ated scales (17), one of two groups of sub- 

 jects made significantly fewer reversal reading 

 errors with the staircase. The second group 

 of subjects, composed of pilots familiar with 

 conventional scales, appeared to take some 

 time to learn the use of the staircase, for 

 only in the second half of the experiment did 



