INSTRUMENTS FOR PRESENTING QUANTITATIVE DATA 



91 



but a combination of a single pointer for the 

 fine scale running to 1 ,000 feet and a counter 

 for the coarse record in thousands of feet 

 was about four times as fast and much less 

 subject to 1,000-feet errors. Grether's data 



established by general opinion that pointers 

 should not be so long that they obscure the 

 graduation marks (93). Thus, common 

 practice is to make the pointer just long 

 enough for its tip to touch the inner edge of 



CONVENTIONAL 



MODIFIED 



PERCENT ERRORS OF 



1.000 FEET OR MORE 



INTERPRETATION TIME 

 IN SECONDS 



THREE POINTERS THREE POINTERS 





7.1 

 7 5 



174 



tg.9 



B% 



TWO 

 POINTERS 



n- 



Bt« 



5.3 



SINGLE POINTER 

 PLUS COUNTER 



18;? 



BV.8 



SINGLE POINTER SINGLE POINTER. 



LEGEND 

 ■i 97 AAF PILOTS 

 CD 79 COLLEGE STUDENTS 



PLUS 

 WINDOW 



TWO 



DIALS 



^V\ ' M^ 



' 6 *~ 



3-»" 



VARIABLE RANGE 

 OF SCAtE 



i^ \ 



''<f. 



\S 3C 



5 Iv^^^ 



VERTICAL SCALES COUNTER 



7.6 00 I 



PERCENT ERRORS OF 



1.000 FEET OR MORE 



INTERPRETATION TIME 

 IN SECONDS 



14 5 

 12 9 



6 3 

 69 



H« 



13.6 



6.0 



10.3 

 I 4 



B23 

 1.9 



R'-' 



1.5 



B"- 



19 



8:3 



00 

 00 



Fig. 11. Reading altitude from different types of instruments. Data from Grether (31) for 176 sub- 

 jects, each of whom made 12 readings on each type of instrument. The results given below each illus- 

 tration show the percentage of readings which were in error by 1000 feet or more and the instrument 

 .". ',erpretation time in seconds. The latter was assumed to be zero for the counter, so counter-test 

 time, essentially number-writing time, was subtracted from all other instrument test times to obtain 

 their interpretation times. 



are summarized in Fig. 11. Development 

 along these hnes is promising. 



Pointer or Index Design. In comparison 

 with problems of scale details, problems re- 

 lated to pointer or index design have received 

 very little research attention indeed. On 

 the subject of pointer length, it has been 



the shortest scale graduation mark. Re- 

 garding pointer width, Loucks (52) and 

 Kappauf, Smith, and Bray (40) offer evi- 

 dence w^hich suggests that narrow pointers 

 may be used with no loss in reading accuracy 

 and with the specific advantage that they do 

 not conceal instrument numbering. Loucks 



