A key part of display design is to translate process data into useful information. This can entail anything from supplying structure to the data to ease interpretation to actual conversion of units (e.g., translating inches in a tank to gallons). Like much in human factors, data translation often requires a trade-off to be made, which inherently has a gain and a loss.
Christopher Wickens of the University of Illinois (Urbana- Champaign) eloquently set forth the principle of display proximity, which states that in integrating data together, it becomes more difficult to utilize the individual components. This concept can be seen readily in data translation. In many processes, a ratio of components needs to be met or maintained. The accompanying figure shows an example of the ways in which this data can be presented. In examining the extremes, either the individual component flows could be shown (A), thereby requiring the operator to mentally divide the values to arrive at the ratio (high potential for error), or the ratio only is calculated and displayed for the operator (B). In the latter case, while the information is better matched to the task (Am I on ratio?), lost are the individual component flows. A proportional drop-off of each flow could still produce the correct ratio.
Analog presentations of the information are shown in C and D. With C, the operator is still required to mentally determine the ratio. Option D, however, uses different scaling of the analog bars so that, when the correct ratio is achieved, both analog bars will be the same length. While the exact values are not easy to determine, the operator can see the individual parameters, as well as evaluate the ratio.
Obviously some combination of these representations can be provided. What is important is to understand that a tradeoff is often required in presenting the operators the information they need. Optimal information for one task is likely to be sub-optimal for another. Displays created for process overview will likely need to be different than those for detailed control, and vice versa. High data translation representations could be used on overview displays, with more detailed data provided at a lower level operating display.
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