1 VISUAL DISPLAYS OF DYNAMIC INFORMATION Things in our world keep changing (such as temperature and blood pressure). This lecture will deal with the design of displays used to represent dynamic information. Quantitative Visual Displays Their objective is to provide information about the quantitative value of a variable. Static variables such as length are also covered in this section. The level of precision required characterizes the concept of the scale unit. Basic Design of Quantitative Displays: Conventional quantitative displays are mechanical devices of one of the following types:

2 1.Fixed scale with moving pointer 2.Moving scale with fixed pointer 3.Digital display The first two are analog indicators. The position of the pointer is analogous to the value it represents (see figure 5.1). Comparison of Different Designs: Many studies have compared different types of conventional quantitative scales. The studies have yielded some different results. But there are still some general suggestions. For example, digital displays are generally superior to analog displays when the following conditions apply: 1) a precise numeric value is required and 2) the values shown remain visible long enough to be read. Analog displays have advantages in other circumstances. For example, fixed-scale moving-pointer displays are useful when the values change frequently or continuously. This change would make the time limited in showing the values if digital displays were used.

3 Another advantage of analog displays is clear when it is important to know the direction or the rate of value change. six factors are offered by Heglin (1973) in considering the selection of analog displays: 1)In general, a pointer moving against a fixed scale is preferred. 2)If numerical increase is typically related to some other natural interpretation, such as more or less or up and down, it is easier to interpret a straight line (horizontal or vertical scales) or thermometer scale with a moving pointer. The pointer position relative to the zero adds an indication to the value. 3)Different types of pointer-scale indicators should not be mixed when they are used for related functions. This will avoid reversal errors in reading.

4 4)If manual control moves the element (pointer or scale), the control should move the pointer (not the scale). 5)If slight variable movements or changes in quantity are important to the observer, they will be more clear if a moving pointer is used. 6)If a numerical value is needed to be readily available, a moving scale appearing in an open window can be read more quickly. Despite of the various advantages of having moving pointers on fixed scales. There are some limitations. If the range of values is too great to be shown on a relatively small scale, a moving scale with a fixed pointer is preferred. Research and experience tend to favour circular and semicircular scales over vertical and horizontal scales. But in some cases, vertical and horizontal scales are preferred.

5 Specific Features of Conventional Quantitative Displays The ability of people to make visual discrimination is influenced (in part) by the specific features to be discriminated. These features include:  Numeric Progressions of Scales: Every numeric scale has a numeric progression system characterised by the numeric difference between adjacent markers on the scale and by the numbering of the major scale markers. In general, progression by 1s (0,1,2,3,…) is the easiest to use. This is the same as a scale with major markers at 0,10,20,30,…., with intermediate markers at 5,15,25,35,…., and with minor markers at individual numbers. Progression by 5 is also satisfactory and by 25 is moderate. Decimals make the scales more difficult to use. If used, the zero before the decimal should be omitted. Unusual progressions (3s,, 7s etc) should be avoided except under very special circumstances.

6  Length of Scale Unit: It is the length on the scale that represents the smallest numeric value to which the scale is to be read. For example, if the force is to be measured to the nearest 10 Newton's then 10 N is the smallest unit of measurement. The scale will be constructed that a given length (in inches, millimeters, etc) represents 10 N of force. The length of the scale unit should permit distinctions between the values with optimum reliability in terms of human sensory and perceptual skills. The research suggests values ranging from about 1.3 to 1.8 mm. Larger values are needed when the use of instruments is not in the ideal conditions (below normal vision, poor illumination, time pressure, etc).

7  Design of Scale Markers: It is recommended to include a scale marker for each scale unit to be read. General accepted design features are shown in figure 5.3  Scale Markers and Interpolation: If scales were to be much compressed, the scale markers will be crowded together which may affect the reading accuracy. It is better to use a scale that does not require interpolation. When high accuracy is needed, a marker should be placed at every scale unit. This will require a larger scale or a closer viewing distance.  Design of Pointers: It is recommended to use pointed pointers (with tip angle of about 20°); have the pointer tip meet, but not overlap, the smallest scale marker; have the color of the pointer extend from the tip to the center of the scale; and have the pointer close to the surface of the scale (to avoid parallax).

8  Combining Scale Features: The previously mentioned features of quantitative scales have been integrated into a relatively standard formats. The above features should be considered as general guidelines.  Scale Size and Viewing Distance: All the previous guidelines are for normal viewing distance (28 inch or 71cm). If a display is to be viewed from far distances, the features have to be enlarged in order to maintain the same visual angle. The following formula could be used to find the proper dimension for a given distance x: Dimension at x in = Dimension at 28 in * (x in/28)

9 Qualitative Visual Displays The main interest is in the approximate value of some continuously changeable variable or in its trend, or the rate of change. Quantitative Basis for Qualitative Reading Quantitative data may be used as the basis for a qualitative reading in three ways: 1)To determine the status or condition of the variable in terms of each of a limited number of predetermined ranges (cold, normal, or hot). 2)To maintain some desirable range of approximate values (speed range). 3)To observe trends, or rates of change (ascending or descending airplane, or north, south, east and west). Qualitative displays are different than quantitative displays in their design (suggested by research). See table 5.1.

10 Design of Qualitative Scales Many qualitative scales have the values sliced into a limited number of ranges. The perception of the correct reading is aided by some method of coding the separate ranges. A possible way of doing this is by using color codes (see figure 5.10). Another way of coding is to use a shape coding system to represent specific ranges of values. It is advised to take advantage of natural compatible associations people have between coding features and the intended meanings. Quantitative displays involve the additional process of assigning the value read to one of the possible ranges of values that represent the categories. However, qualitative displays directly convey the meaning of the display indicator.

11 Check Reading It refers to the use of an instrument to make sure whether the reading is normal. This is usually done using a quantitative scale. But the normal condition is represented by an exact or very narrow value rather than a range. This requires greater attention to display clearly the normal reading. Research suggests that the normal reading position should be aligned at the 9 o’clock position (or 12 o’clock). See figure Status Indicators Some times qualitative information indicate the status of a system. However, status indications show separate, discrete conditions such as on/off or stop/caution/go. If this is the case, the instrument could be converted to a status indicator (lights). Redundant codes could be used (color and position). It is possible to use other coding systems such as marks on the oven controls.

12 Signal and Warning Lights Lights in steady state or flashing could be used for various purposes (warning, identification, attention attraction, etc). Factors affecting the detectability of lights are listed below:  Size, Luminance, and exposure time Detecting a flashing light depends on a combination of size, luminance, and exposure time. The larger the light and/or the longer the exposure time, the lower the luminance required to detect the light. (see figure 5.13).  Color of Lights The background color and the ambient illumination can interact to influence the ability of people to detect and respond to lights of different colors. With low signal-to-background brightness contrast, a red signal is recommended. Green, yellow, and white follow in the recommendation.

13  Flash Rate of Lights The flash rate should be lower than 30 times per second. (WHY?) It is recommended to have flash rates of about 3 to 10 per second (with duration of at least 0.05 s) to attract attention. 60 to 120 flashes per minute (1 to 2 per second) are recommended for use in highways and flyways. Most of the times, the flashing rate is fixed. However, some cases require the use of lights with different flash rates to signify different things. (to show the rate of deceleration while applying a break to the car). In this regard, it wise to remember that humans can differentiate three different flash rates (maximum) clearly.