The study of dial legibility in terms of accuracy of reading has been carried on from two approaches. In one of these the dial shape is varied, while the graduations are held constant. The other approach is to hold shape constant and to vary the number of graduations. The present study presents a combination of the two earlier approaches, with shapes and graduations both being varied. Sixty dials were presented in booklets to forty Ss, who read them to the nearest 0.1 cm. while being timed. The results indicate that in dial reading situations where exposure time is not limited there is a significant difference among graduations but not among dials

Black, Bruce B.

Fluger, Dorothy

Karas, George G.

English

University of Northern Iowa

Proceedings of the Iowa Academy of ScienceVolume 69 | Annual Issue Article 761962Dial Legibility as a Function of Scale Graduationand Dial ShapeBruce B. BlackIowa State UniversityDorothy FlugerIowa State UniversityGeorge G. KarasIowa State UniversityCopyright © Copyright 1962 by the Iowa Academy of Science, Inc.Follow this and additional works at: https://scholarworks.uni.edu/piasThis Research is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academyof Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu.Recommended CitationBlack, Bruce B.; Fluger, Dorothy; and Karas, George G. (1962) "Dial Legibility as a Function of Scale Graduation and Dial Shape,"Proceedings of the Iowa Academy of Science: Vol. 69: No. 1 , Article 76.Available at: https://scholarworks.uni.edu/pias/vol69/iss1/76Dial Legibility as a Function of Scale Graduation and Dial Shape BRUCE B. BLACK, DOROTHY FLUGER, AND GEORGE G. KARAS1 Abstract. The study of dial legibility in terms of accuracy of reading has been carried on from two approaches. In one of these the dial shape is varied, while the graduations are held constant. The other approach is to hold shap constant and to vary the number of graduations. The present study presents a combination of the two earlier approaches, with shapes and graduations both being varied. Sixty dials were presented in booklets to forty Ss, who read them to the nearest 0.1 cm. while being timed. The results indicate that in dial reading situations where exposure time is not limited there is a significant difference among graduations but not among dials. Studies of Sleight ( 1948) and Graham ( 1956) set a pattern for investigations of dial legibility as a function of dial shape. Sleight tachistoscopically presented dials drawn with India ink on white paper. He used a standard scale length, equal propor-Uuns, identical numbers, and movable pointers. He defined legi-bility in terms of the percent of errors for each design. In his summary of studies done during World War II, Sleight pointed out: that mid-division lines which changed from one part of the scale to another increased error, that accuracy decreased as the number of scale divisions increased, that numbering of scale sub-divisions tended to increase accuracy in timed exposures, that the starting point of a scale did not affect legibility, and that reduction in width of a pointer which blocked markings did not improve accuracy. Graham's ( 1956) study indicated that horizontal dials were more easily read correctly than were cir-cular or vertical dials when presented in a tachistoscope. Grether ( 1949) solved the problem of how to present efficient-ly a large number of dials to many subjects at once by prepar-ing printed booklets with the dials arranged in a random fashion through the booklet. Grether's study was of dial legibility as a function of scale graduation. He found that the booklet presenta-tion was as reliable as tachistoscope presentation for his type of study. The earlier studies have generally limited the variables to ei-ther dial shape or scale graduation, with the other variable held constant. The results of Sleight's ( 1948) study, for example, show that the most legible dial shape is the open-window, followed by 1 Department of Psychology, Iowa State University, Am.,,., Iowa. 486 1Black et al.: Dial Legibility as a Function of Scale Graduation and Dial ShapePublished by UNI ScholarWorks, 19621962] DIAL LEGIBILITY 487 the round, semi-circular, horizontal, and vertical, with percent errors from 0.5 per cent to 35.5 percent. McCormick ( 1957) re-ports that Kappauf, Smith and Bray have shown that dials grad-uated by five's are read more accurately than those graduated by one's or ten's, with percent errors ranging from 13 percent to 25 percent. The difference between five's and one's was not significant, while the difference between either five's or one's and ten's was highly significant. McCormick also cites a study by Vernon, in which greatest accuracy in reading was with a scale graduated for each of the scale units to which the scale is to be read. Other studies have dealt with the scale graduation variable and legibility ( Chapanis, 1947; Y eyzorek, 1949; Chapan-is and Leyzorek, 1950) with similar conclusions. The purpose of the present study was to determine the exact relationship between scale graduations, dial shapes, and the leg-ibility of the dials. The objective was to test whether or not the findings of the earlier research could be replicated in a study which, by design, combined the two variables, shapes and grad-uations. Legibility was defined in terms of accuracy in reading. The design read with the smallest percent error was taken to be the most legible. Fifteen dial designs were prepared using the five dial shapes found by Sleight to be the most common, and the three methods of graduating the scales of the dials as reported in Kappauf, Smith, and Bray. On the basis of the past studies, it was hypothosized that the open-window dials would be more legible than the other shapes, and that the one-unit interval grad-uation (every 0.1 cm. marked) would be more legible than the five-unit graduations. METHOD Subjects The forty male subjects who participated in the study were volunteers from an introductory psychology class. Their ages ranged from seventeen to twenty-five. Subjects were tested in groups of from five to eight. In response to the questions on the cover page of the booklet, one subject responded that he did not drive a car, and five of the thirty-nine card drivers had some dial reading experience beyond auto or tractor driving. One of these five was an airplane pilot, while the otheir four had worked in quality-control or measurement jobs. These five subjects with job-connected dial reading experience performed no better than the rest of the group. Stimulus Material Each subject was given a test booklet of seven pages. The cover page presented instructions for reading the dials and ques-2Proceedings of the Iowa Academy of Science, Vol. 69 [1962], No. 1, Art. 76https://scholarworks.uni.edu/pias/vol69/iss1/76488 IOWA ACADEMY OF SCIENCE [Vol. 69 tions regarding biographical information. Inside the booklet were sixty dials, two dials of each type on each page. Each diaf s scale was ten centimeters long, and was numbered from 0 to 10. The scale markers were: for graduations placed at 1.0 and 0.5 cm., 1/8 inch long; for graduations at 0.1 cm., 1/16 inch long. The five shapes used were: open-window, vertical, round, semi-circular, and horizontal (Sleight, 1948). All dials on a page were graduated in the same manner, with markers at each 1.0 cm., each 0.5 cm., or 0.1 cm. Pages were shuffled in the assem-bly so that no two consecutive pages were graduated in the same manner. A standard pointer, 1/16 inch wide and 9/16 inch-es long, was used on every dial. The sixty readings which were indicated by the pointers were drawn from a table of random numbers ( Snedecor, 1959). Procedure Each subject was requested to complete a personal informa-tion questionnaire which included these questions: "Do you drive a car?", "Have you ever had a job which caused you to read dials?", and "Where?". The experimenter read the printed directions aloud, then requested that the subjects read the sam-ple semi-circular dial to insure that the directions were under-stood. The experimenter started the subjects simultaneously and timed them. Subjects were given all the time they required to complete and check their booklets. A key, prepared from the original pointer settings on the dials, was used for scoring the responses. The percent error was com-puted for each dial and these percents were transformed to the arcsin for purposes of data analysis. RESULTS AND DISCUSSION The analysis of variance performed on the transformed data is shown in Table 1. It can be seen that the main effect for graduations produced an F significant beyond the .01 level. The dials graduated every 0.1 cm. were most legible ( 12.5% error). The 0.5 cm. graduations were the next most legible ( 16.1% error the 1.0 cm. graduations were the least legible ( 35.0% error). It should be noted that the difference between 0.5 cm. graduations and 0.1 cm. graduations was not significant. These results cor-respond closely to the finding of earlier investigators and sup-ported that portion of the second hypothesis which stated that the one-unit graduations would be more legible than the ten-unit graduations. They did not support that part of the hypothesis which predicted greater legibility for the one-unit graduations than for the five-unit graduations. Neither the shape main effect nor the interaction between graduations and shapes was significant. The non-significant 3Black et al.: Dial Legibility as a Function of Scale Graduation and Dial ShapePublished by UNI ScholarWorks, 19621962] DIAL LEGIBILITY 489 Table 1. Analysis of variance of percent errors transformed to the arcsin. Source Degrees of Freedom Mean Square Graduations ( G) 2 1228. 700 Shapes ( S) 4 130.5 G by S 8 315.4 Error 45 216.9 "" Significant beyond the .01 level. main effect for shape was not expected in view of the marked differences in shape legibility found by such investigators as Graham ( 1956) and Sleight ( 1948). It should be noted that the present study employed a different stimulus presentation meth-od (booklet vs. projected movies or tachistoscope) and a longer exposure time per stimulus (unlimited exposure time with the minimum being 3 to 4 seconds vs. fractions of a second). Sleight ( 1948) indicated that restriction in exposure time to 0.12 seconds was necessary to produce a high enough error rate for his in-vestigation. It was pointed out earlier that the booklet presenta-tion method was as satisfactory as other techniques when used for determining the effects of different scale graduations on legi-bility. However, it does not appear appropriate for investigation of the shape variable in the light of the long exposnre times in-herent in using the technique. A more adequate test of the effect of combining the two variables would seem to necessitate the use of limited exposure times. The main implication of the pres-ent study, therefore, would be that in dial reading situations where exposure time is not limited, the shape of the dial is irrel-evant. Broader conclusions await a test of the type indicated above. Literature Cited Chapanis, A. Accuracy of interpolation between scale markers as a function of scale interval number. Amer. Psycho!., 1947, 2, 346-349. Chapanis, A. and Leyzorek, M. Accuracy of visual interpolation between scale markers as a function of the number assigned to the scale interval. J. exper. Psycho!., 1950, 40, 655-667. Graham, N. E. The speed and accuracy of reading horizontal, vertical, and circular scales. J. appl. Psycho!., 1956, 40, 228-232. Grether, W. F. Instrument reading. I. The design of long scale indicators for speed and accuracy of quantitative readings. J. appl. Psycho!., 1949, 33, 363-372. McCormick, E. J. Human engineering. New York: McGraw Hill, 1957. Sleight, R. B. The effect of instrument dial shape on legibility. J. appl. Psycho!., 1948, 32, 170-188. Snedecor, G. W. Statistical methods. Ames, Iowa: Iowa State College Press, 1959. 4Proceedings of the Iowa Academy of Science, Vol. 69 [1962], No. 1, Art. 76https://scholarworks.uni.edu/pias/vol69/iss1/76

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