Document kgXQGpNZbGJbGdm9KqBooxx0

88 BOSS A. MC FARLAND the numbers and dial markings and mark off this range by heavy lines on the dial circumference. The operator then merely notes whether his pointer is within, above, below, or moving in a particular direction with regard to this range. This type of instrument is termed a qualitative display. A group of dials of this type may be arranged in a pattern to show at a glance which of several instruments may be malfunctioning. For this purpose thqy should be arranged in rows or columns so that their normal operating range is similar (see Figure 7) .24 The third and con- Pttterntd Dial Display Unpatterned Dial Display Figure 7. Patterned and unpattemed dial displays. Dials that are only required to indicate whether or not a certain activity is within a normal operating range may often be grouped together in a patterned display in which the normal pointer readings are oriented in the same direction. A quick glance can then determine which of many activities has departed from normal, as in the display at the left. In the unpatterned display at the right a much-.more time-consuming examination is necessary. (From Chapanis et al.") ventional type of indicator is called a quantitative display. Here the worker finds a;reads tue display, ASdH;8peettWte'ladW'pi'.f\V.,iu.,eMdicS can give not only the 'directibh!but''thd`Ste,;'of-change as well. In many cases a quantitative indicator could be replaced by one of :the other types. This sort of redesign should be one of the first considerations in, the Fumn~enpneerTng`1i5f"Tisua];`',i'dispIays.'2"=:VVhen-'quantitatives'displayS'.arefcUsed^ however, they may consist of either a moving pointer with a fixed scale or a moving scale with a fixed pointer. For general purposes the former is most advantageous.48 i " C. A. Baker and W. F, Grether, Visual presentation of information, WADC Tech. Repl.. 64-I6O, Wright Air Development Center, Wright-Patterson Air Force Base, Ohio, 1954. ' HUMAN ENGINEERING AND INDUSTRIAL SAFETY 89 4- Principles of Display Design |j$W" In addition to general factors involving the visibility of objects within the forking area, sufficient-research has been done within the field of visual display llgsign to warrant some fairly specific recommendations. The areas of research J|l|clude shape, size, type of scale markings, distance between markings, type of J||||iqinter, direction of increase on scale, and the design of multirevolution instru- wt^'piments. Some of the more important findings are summarized below. Shape of Dial. The five most commonly used dial shapes have been ex- '^vjp-piirimentally tested for accuracy of reading by Sleight. All were equated in terms S Satof size and shape of numerals, illumination, and so forth, so that any differences in f|S$g accuracy may be presumed to be primarily due to shape. The shape found (|iye the fewest reading errors in this test was the open window type of direct 5i:ling counter. Mistakes were made in only 0.5 per dent of the readings. The fmost accurate dial, although very much inferior to the open window type, was |i|pnd or circular type; 10.9 per cent of errors were observed with this display... TiisSj^g, in order of mistakes, were the semicircular dial, 16.6 per cent; the ||al, 27.5 per cent; and finally the vertical shape with 35.5 per cent errors.47 lig marked superiority of the direct reading counter is evident only under ivqns of rapid viewing during short exposure. Where the viewing time may be _|ffened, the number of errors observed in the other types of dials would be ^^feibstantially reduced. Also, for check reading in a group of instruments ^(^^e-8-7-)"the-moviiig-poirtter'type of- display-is definitely superior. Jwe of Dial. The optimum size of the dial is, of course, related to the viewing el For a distance of 30 inches between the display and the eyes of the tyt has been found that a dial 3 inches in diameter can be read faster and Jslerverrors than dials of smaller size. The diameter must be increased for |||r above 30 inches and. decreased for those below 30 inches.48,49 An addi- |^|iable, however, is the number of scale markin^or indices that.must be |a%.5..shows the minimum .dial diameters underj.varying conditions. No froutdtbe less than 1 inch in diameter regardless of the circumstances.90 ^HiMe Markings and Numberings. The ease of. quantitative dial reading Mnlly'affected !by scale markings and numbe^ngs. .1`he yfflpycjn p|actice '!jternumbered-division marks'ionger than"the'ha-KwayJ marks'is good, f idings, the fewer the marks the better. When accuracy is desired as Bleight, The effect of instrument dial shape on legibility, J. 'Applied Psychol., 32, ..n,,T948,ir ; ' 'V" retKef7 The'"desigrr6f 'instruments for ease of readihg/Paper^presentefl br.fore v Engrs. National Aeronautic and Air Transport Meeting, April, 1948. , rE Kappauf and W. M. Smith, Design of instrument scales for maximum legibility: J?ff^!:!ji^remninafy experiment on dial size and graduation, Memorandum. Rept. No. MCREXD- i w,,Air Materiel Command, July 12, 1948. /' 14''^^^SlfcWoodson, Human Engineering Guide jor Equipment Designers, JJniversity of umulr^Derkelev, 1954. Uiiflal,lt . , ` '