1. Communication: Displays
Both of the suggested texts, Work Design and Fitting The Task To The Human will be critical for complete understanding of this subject matter. However, the chapter, Human-Machine Systems, from Fitting The Task To The Human presents the critical information in a very concise format. We strongly suggest a very complete understanding of this chapter.

2. Definition Of A Display
A display is an output device that communicates with a human.
A display is an output device that communicates with a human. Displays are not limited to the human – machine interaction but is frequently associated with humans and their interaction with machines within a system. However, items such as magazines, newspapers and signs are also all examples of displays. As described in the recommended text Fitting The Task To The Human, a Human-Machine System’ means that the human and the machine reciprocal relationship with each other. This is a closed loop cycle in which the human holds the key position because the decision rest with the operator. The display provides information about the progress of production; the operator perceives this information and must be able to understand and assess it correctly.

3. Interfaces
The displays providing feedback to the human about the status of the machine of the behavior of the whole system.
The controls by which the operator inputs feed forward affecting the system.
In human-machine systems it is usually a matter of visual presentation of dynamic process. The “points of interchange” (called interfaces) of information and energy from human to machine and from machine to human are of paramount importance to the human factors engineer. Two interfaces are of particular interest:
The displays providing feedback to the human about the status of the machine of the behavior of the whole system.
The controls by which the operator inputs feed forward affecting the system.
This module will focus strictly on the display component of the system.

4. Matching the Display with Information Requirement
It is important that the instrument gives the operator only the information required, for instance by displaying the smallest unit that the operator is likely to read off.
It is important that the instrument gives the operator only the information required, for instance by displaying the smallest unit that the operator is likely to read off. Thus, if there is a need to read pressure to the nearest 100 N, the smallest division should be 100 N.

5. Matching the Display with Information Requirement
Sometimes the operator does not need a precise reading but just to know a range. Here a moving pointer is best and the various ranges should be marked by different color.
Sometimes the operator does not need a precise reading but just to know a range. Here a moving pointer is best and the various ranges should be marked by different color.

6. Dynamic Displays Quantitative Qualitative Exact Information
General Condition or Status
Dynamic displays can be quantitative or qualitative in how they convey information. Quantitative displays show exact information. Digital quantitative displays present information directly as numbers, for example, the clock on your computer. Analogue quantitative displays can also be used where a length or angle represents the information, for example, a thermometer where the length of mercury or alcohol represents the temperature. The use of a particular quantitative display depends on the kind of information that is required. If you need a precise reading, then digital indicators are most easily read.
Qualitative displays give information about particular states, for example, hot or cold, alarm or no alarm. These displays can provide information about rate of change or direction of deviation from a desired value. These displays may include indicators and warning devices. They can be used in circumstances where you only need to know that a certain condition exists, for example, when the temperature is too hot or too cold, as in the case of an indicator light on an iron which goes out when the iron is up to temperature. The specific value is not needed, although that may be conveyed to you by other, quantitative visual displays.

7. Check-reading Displays
Check-reading displays are a specific type of qualitative display in which you determine whether the value of a continuously changing variable is normal, or within an acceptably normal range.
Check-reading displays are a specific type of qualitative display in which you determine whether the value of a continuously changing variable is normal, or within an acceptably normal range, for example, car fuel gauges and tire pressure gauges. Check-reading displays should have clearly distinguishable characteristics to identify the neutral or normal satisfactory condition, or the undesirable condition; perhaps green marking for an 'OK' level and red for 'out-of-limits'.

8. Qualitative vs Quantitative Displays
Fixed scale & moving pointer
speedometer
Fixed pointer & moving scale
analog bathroom scales
Digital display
digital watch
If it is necessary to see how a process is changing, to note the amplitude or direction of some change, then the pointer moving over a fixed scale gives that information most easily.
A scale moving by a fixed indicator mark may also be used for these purposes, but suffers from the disadvantage that it may be hard to memory or assess the previous reading or to assess the extent of the movement.
If a process must be set to some particular value it is easier to do this with a moving pointer because a second pointer or a marker can be pre-set and the process accurately controlled as the two pointers come together.
If the process covers a wide scale range, then the moving-scale instrument will serve better than a moving-pointer display.

9. Digital vs. Analog Displays
Digital Displays
Preferred when precise numeric values are required, legible digits are needed quickly or the value remains stable for a long enough period to be read
If it is simply a matter of reading off the exact value of some quantity, the digital counter window is the fastest and most accurate.

10. Types of Displays Type of Display Moving Pointer
Fixed Marker Moving Scale
Digital Counter
Ease of Reading
Acceptable
Very Good
Detection of Change
Poor
Setting to a Reading or Controlling a Process
This table summarizes the pros and cons with different way of displaying information.

11. Design of Scale Graduations
The height, thickness and distance of scale graduations must be such that they can be read off with minimal likelihood of error, even if lighting conditions are not ideal.
There are seven recommendations for the design of scale graduations. They are summarized as follows:
The height, thickness and distance of scale graduations must be such that they can be read off with minimal likelihood of error, even if lighting conditions are not ideal.

12. Design of Scale Graduations
The information presented should be what is actually wanted: scale divisions should not be smaller than the accuracy required; qualitative information should be simple and unmistakable.
The information presented should be what is actually wanted: scale divisions should not be smaller than the accuracy required; qualitative information should be simple and unmistakable.

13. Design of Scale Graduations
Scale graduations should give information that is easy to interpret and to make use of. It is laborious to have to multiply the reading of the instrument by a factor. If this is unavoidable, then the factor should be as simple as possible.
Subdivisions should be by ½ or 1/5: anything else is difficult to read off.
Scale graduations should give information that is easy to interpret and to make use of. It is laborious to have to multiply the reading of the instrument by a factor. If this is unavoidable, then the factor should be as simple as possible.
Subdivisions should be by ½ or 1/5: anything else is difficult to read off.

14. Design of Scale Graduations
Numbers should be confined to major scale graduations and, once again, subdivisions should be ½ or1/5.
The tip of the pointer should not obscure either the numbers of the graduations and if possible should not be broader than a scale line. It is best if the tip of the pointer comes as close as possible to the scale, without actually touching it.
Numbers should be confined to major scale graduations and, once again, subdivisions should be ½ or1/5.
The tip of the pointer should not obscure either the numbers of the graduations and if possible should not be broader than a scale line. It is best if the tip of the pointer comes as close as possible to the scale, without actually touching it.

15. Design of Scale Graduations
The pointer should be as nearly as possible in the same plane as the graduated scale, to avoid errors of parallax, and the eye must be positioned so that the line of sight is at right angles to the dial and pointer.
The pointer should be as nearly as possible in the same plane as the graduated scale, to avoid errors of parallax, and the eye must be positioned so that the line of sight is at right angles to the dial and pointer.

16. Scale Graduations Height of biggest graduations a/90
Height of middle graduations
a/125
Height of smallest graduations
a/200
Thickness of graduations
a/5000
Distance between two small graduations
a/600
Distance between two big graduations
a/50
Even more important than the shape of the dial itself is the size of the scale graduations. Since lighting and contrast are not always ideal, and other adverse factors are present in a real workplace, we recommend rather big graduations as follows: if a is the greatest viewing distance to be expected, in mm, then the minimum dimensions of graduations should be as follows:
Height of biggest graduations: a/90
Height of middle graduations: a/125
Height of smallest graduations: a/200
Thickness of graduations: a/5000
Distance between two small graduations: a/600
Distance between two big graduations: a/50

17. Background and Lettering
Black letters on a white background are preferred, in principle, because white characters tend to blur, and a black background may set up relative glare against its lighter surroundings.
Black letters on a white background are preferred, in principle, because white characters tend to blur, and a black background may set up relative glare against its lighter surroundings. However, white symbols show up better in poor lighting, especially if the symbols and the pointer are luminous.

18. Text Size Breadth 2/3 of height Thickness of line 1/6 height
Distance apart of letters
1/5 of height
Distance between words and figures
The size of letters or numbers in mm is equal to the viewing distance in mm divided by Capital and lower case letters are easier to read than letters all of the same size. Most letters and numbers should have the following proportions:
Breadth: 2/3 of height
Thickness of line: 1/6 height
Distance apart of letters: 1/5 of height
Distance between words and figures: 2/3 of height

19. Viewing Angle
The preferred angle of view for displays (the angle at which the display plane is positioned with regard to the person monitoring it) should be 90 degrees.
The preferred angle of view for displays (the angle at which the display plane is positioned with regard to the person monitoring it) should be 90 degrees. This is especially important with large picture displays as positioning them at an angle may cause parts of the display to be hidden from your eyes.

20. Analog Display Design Moving pointer on a fixed scale is preferred.
If numerical change relates to natural function (e.g. up/down) then vertical display is preferred to circular display.
Types of pointer-scales should not be mixed to indicate related functions in displays.
Direction of movement of pointer should match that of the control.

21. Analog Display Design
If value must be read quickly then a moving scale appearing in an open-window is best..
Semi-circular or circular displays preferable to horizontal or vertical displays.
Adjacent scales should have similar markings and be oriented to the same point to indicate normal operation. This is exemplified with check scales

22. Analog Displays: Scale Markings
Marker length depends on level of illumination - markers must be thicker and farther apart in low light.
Markings should be presented for the smallest scale unit that needs to be read.
Use different interval markers (in gradations like a ruler).
Zero should be placed at 6 o'clock or 12 o'clock (standard for auto industry is 7 o'clock however)

23. Analog Displays: Numerical Progression
Intervals of 1 are easiest to read (0, 1, 2, ...)
Decimal progression is the second most preferred (10, 20, 30,...)
Units of 5 is the next best (5, 10, 15, ...) intervals of 2 are also OK(2, 4, 6, ...)
Avoid unusual progressions (e.g. by 3, by 7, by 8)
Scale intervals should represent consistent progressions (all intervals should equal the same amount)
Intervals of 1 are easiest to read (0, 1, 2, ...)
Decimal progression is the second most preferred (10, 20, 30,...)
Units of 5 is the next best (5, 10, 15, ...) intervals of 2 are also OK(2, 4, 6, ...)
Avoid unusual progressions (e.g. by 3, by 7, by 8)
Scale intervals should represent consistent progressions (all intervals should equal the same amount)

24. Control and Display Rules
Controls and instruments which are functionally linked should make corresponding movements that comply with our own stereotypes.
Obviously there is overlap between controls and displays. We will briefly discuss some rules for controls and displays and how they should function together. These principles are not cultural specific and are applied all over the world. The first principle is that controls and instruments which are functionally linked should make corresponding movements that comply with our own stereotypes.

25. Control and Display Rules
When a control is moved or turned to the right, the pointer must also move right over a round or horizontal scale; on a vertical scale the pointer must move upwards.
When a control is moved upwards or forwards, the pointer must move either upward or to the right.
Some rules can be summarized as follows:
When a control is moved or turned to the right, the pointer must also move right over a round or horizontal scale; on a vertical scale the pointer must move upwards.
When a control is moved upwards or forwards, the pointer must move either upward or to the right.

26. Control and Display Rules
A right-handed or clockwise rotation instinctively suggest an increase, so the display instrument should also record an increase.
A right-handed or clockwise rotation instinctively suggest an increase, so the display instrument should also record an increase.

27. Control and Display Rules
A moving scale with a fixed pointer indicator should move to the right when the control is moved to the right but the scale values should increase from right to left, so that a rotation of scale to right gives increased readings.
Hoyos (1974) recommended that a moving scale with a fixed pointer indicator should move to the right when the control is moved to the right but the scale values should increase from right to left, so that a rotation of scale to right gives increased readings.

28. Control and Display Rules
When a hand lever is moved upward, or forward, or to the right, the display reading should increase or the equipment should be turned on. To reduce the reading, or to switch off, it is instinctive to pull the lever toward the body or move it to the left, or downward.
When a hand lever is moved upward, or forward, or to the right, the display reading should increase or the equipment should be turned on. To reduce the reading, or to switch off, it is instinctive to pull the lever toward the body or move it to the left, or downward.

29. Conclusion Good Visibility Good Comprehension Good Compatibility
See it
Good Comprehension
Make correct decisions
Good Compatibility
Easily used with others
As you study the information in this module it may help you to keep the three following principles in mind: Displays will generally be effective if they have:
Good visibility - you can easily and clearly see the displays. To attract attention visually, the display must be within your field of vision and should flash or change in some other way. Humans are very good at detecting movement.
Good comprehension – you can make the correct decisions and control actions with minimum effort and delay, and with as few errors as possible, because you have understood the displayed information.
Good compatibility - the display can be used easily with others and you are not confused by any different types used. It can easily be seen and understood in the space and lighting in which it is used. The movement and layout of displays matches those of their controls.