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Design of Instrument Dials for Maximum Legibility. Part 5. Origin Location, Scale Break, Number Location, and Contrast Direction

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This report deals with an investigation of the effects which origin location, scale break, number location, and contrast direction have upon the speed and accuracy of dial reading. Specific errors which are examined and discussed include reversal errors and errors of plus one numbered scale division. The data are based on a total of 40,400 readings contributed by 46 subjects tested in a group testing situation. Within the limits of design variation studied, the results indicate that the best design for a simple dial which is to be numbered every 10 units and read quantitatively at any and all scale values, is one which has a scale break at zero, locates the zero near the bottom of the dial, and locates the numbers outside the scale. At daytime illumination levels like those used in the present experiment, it makes no difference whether the dial is of black-on-white or white-on-black design. Both the error of plus one numbered division plus 10 units in the present case and the reversal error are found to be associated with the reading habit of consulting the scale number which is nearest the pointer. The plus 10 units error is most common in the numerical scale region 0 to 9 no matter where that region appears on the dial. The reversal error is more common in the lower half of clockwise dials where the scale proceeds from right to left than in the upper half where the scale precedes from left to right.

Subject Categories:

  • Flight Control and Instrumentation
  • Human Factors Engineering and Man Machine Systems

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