96 



DESIGN AND USE OF INSTRUMENTS 



they have for these instruments just de- 

 scribed. 



Summary 



Experiments deahng with the marking, 

 illumination, and detailed design of instru- 

 ments have been reviewed. It has been 

 observed that in each area of study there are 

 still questions to be answered. Many 

 studies need repetition because of the small 

 number of subjects for whom data have been 

 reported. Other studies have been hastily 

 run and remain incomplete. 



Problems of instrument illumination are 

 reasonably well in hand. The merits of 

 counter-type indicators have been well ex- 

 plored. Problems of graduation-mark spac- 

 ing and interval values are currently under 

 further investigation. Particularly needed 

 are new investigations of direction of con- 

 trast effects, of pointer and index designs, 

 and of the relative merits of different scale 

 forms both for quantitative and for check 

 reading operations. Such research, which 

 to date has only been carried out at high 

 levels of illumination, should be extended to 

 determine whether different design require- 

 ments prevail for instrument use under low 

 level red illumination. 



References 



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2. Backstrom, H. Die Dezimalgleichung beim 



Ablesen von systemtrischen Skalen, ihre 

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