Ergonomics 4 Schools

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Visual Displays

Visual displays What is a visual display?

A visual display is a device that presents information about objects, events or situations, to you through your eyes. Sometimes the display will be used in addition to information gained by observing the event or situation directly, but in some circumstances the display may be the only source of information available to you.

Examples include TV, your computer screen, thermometers, car instruments, charts, graphs, maps and other forms of printed or written material.

There are also displays that make use of your other senses:

Auditory - where information is presented to you via your ears. These displays are good at attracting your attention when vision can't be used (at night or with someone with limited sight, for example). Because of the ability of audio alarms to attract attention, they are often used to draw your attention to something (a car indicator clicking), and as emergency alarm systems (a fire alarm).

Tactile - where information is presented to you via your sense of touch. The human tactile system is not as sensitive to differences or changes in stimulus as either the visual or auditory systems. An example of a tactile display is the Braille alphabet for the blind. The tactile sense can also tell you subtle information like temperature or surface condition (wet, sticky, slimy etc.) Have you ever felt a radiator to see if it is warming up?

Some items can combine all three forms of display - your mobile phone is one example. You can read text messages from the screen, you can hear it ring and you can feel it vibrate!

 

Effective visual displays

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.

 

 
 
  Types of display

Displays can be classified according to their physical characteristics (what they look like), or according to the type of information that they provide (what they are telling you).

Classification according to physical characteristics:

 
 

DIALS

    

Dials have a graduated scale on which the indication of a value is shown by a pointer.

INDICATORS

    

These displays have no graduated scale, but display text or numeric information, or show the state of a system.

WARNING DEVICES

Warning displays call for your attention and will require you to take some action, for example, a red traffic light means that you must stop your vehicle.

 

COUNTERS

Counters show information directly as numbers.

 
  Classification according to type of information displayed:  
  QUANTITATIVE DISPLAYS

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

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.

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 tyre 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'.

REPRESENTATIONAL DISPLAYS

These displays can portray either working models or simplified diagrams of a complex process, system, or machine. They enable you to perceive the functioning of each part of the system or machine in correct relation to the whole system. London Underground and Ordnance Survey maps, and railway signal box mimic diagrams are examples of representational displays. 

Representational displays should aim at schematic representation of information (keep it simple) rather than a complete representation or the actual representation.

The well-known London Underground map is an example of representing the geographic situation by a stylised and clearer design. The exact geographic inter-relationships of stations are replaced by a colour-coded series of lines which convey the structural layout of the system and make it easier for you to plan your route.

 
 
 

? ? ? ? ?

ANALOGUE
v
DIGITAL

An ANALOGUE display generally shows a pointer and a scale. The position of the pointer on the scale continually corresponds to the value that the display represents.

A DIGITAL display shows information directly but as distinct values.

If rates and direction of change are needed then an analogue display may be more suitable than a digital display. If precise readings are needed quickly then a digital display may be better.

 

 

? ? ? ? ?

QUANTITATIVE
v
QUALITATIVE

If something is QUANTITATIVE, it means that it is capable of being measured - it has a quantity.  A quantitative display provides information about a value. For example, a quantitative speed reading would show that you are driving at 30 miles per hour.

If something is QUALITATIVE, it means that it is has a certain distinct feature - it has a quality. A qualitative display can provide information about the rate or direction of change, or about the state of a system (e.g. on or off). For example, a qualitative speed reading would show that you are slowing down or speeding up.

 

 
 
 
 

 
Design guidelines for displays
 

GENERAL GUIDELINES

Viewing distance
The maximum display viewing distance should be determined by the size of details shown on a display. The reading distance for displays is usually 300-750mm, as many displays have to be read at arm's length and must allow you to reach or adjust controls. Displays must be optimally positioned within your field of view.
 

Illumination
Displays may have their own internal or back-lighting, but if not, their design should be suited to the lowest expected lighting level.
 

 

Angle of view
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.
 
Combinations of displays
For these complex displays you will almost invariably have to divide attention between a number of tasks, as well as the displays themselves. Any inconsistencies in the manner of information-representation among the displays will be confusing, and will reduce your speed of reaction to a change indicated by a display, or even cause reading or decision errors. If a number of displays look alike, you may interpret data incorrectly. Each display should be easily distinguishable, and its information not easily confused with that on any other display.
 
Compatibility with related controls
Displays and their associated controls should be designed and located so that you can select the correct control and operate it effectively and without error. 
 
Quantitative display

SPECIFIC GUIDELINES

Quantitative displays
The scale must be legible and you should avoid multiple or non-linear scales. Scale numbers, marking strokes, pointers, etc., should contrast well in tone and colour with the display face. This should be combined with good illumination and the absence of glare or reflections. You should also position the dial near eye level and approximately at 90 degrees to your angle of view. Scale numbers should increase clockwise, left to right, or upward.
Legibility is the most important design factor. A simple rule of thumb which works well for average quality of lighting and eyesight and with sensible typefaces, is the '1 to 200 rule'. Estimate where the display is to be read from, measure the distance from the eye to the display and divide by 200. You now have the height of the capital 'E' you need. So if a display is to be read from 5m then the letter height should be 5000/200mm = 25mm. If the distance is 400mm, as might be the case for a computer screen, then 2mm will work fine. This rule-of-thumb can also be used to establish the lettering size and the significant divisions for analogue displays.
Try this Create a document containing different sizes of random letters and numbers and print out. Hold this up towards the end of a corridor and see when people can accurately read what you are displaying. Don't forget to use some older people as their eyesight (even when 'corrected' with glasses or contact lenses) is not as good as yours! The reason for random letters is that we read and predict words and 'fill in' for anything that is not clear. 
You should also note that people are not reliable in reading and remembering long strings of digits. Therefore you should limit a digital display to 6 or 7 numbers, and for repeated observation, to 4 numbers. Perception and memorability of digits can also be enhanced by grouping them into pairs, leaving space between adjacent digits. (This 'chunking' of numbers helps you to remember your telephone number.)
 

Qualitative display Qualitative Displays
Each of the displayed conditions should be as distinctive as possible, through differences in position, colour, shape or size on the display. You should integrate more than one of these means on the display, for example, by using lights combined with a change in position of the indicator. The fuel gauge in a car might, for example, flash when the tank is nearly empty. The different rings on an office phone for internal and external calls is another example of a qualitative alarm.
Straight, vertical dials are recommended for observing qualitative direction of change. Circular dials seems to be better for observing rate of change because the angle of the pointer will quickly tell you information about the rate of change.
If designing in a complex environment, such as a power station control room, you must make sure that only the minimum of audio warnings and alarms are triggered. Too many can be confusing and can increase the time taken to react to what could be a critical situation.
 
Animated displays Try thisDisplay example
Do you think that this set of displays could be confusing? Why? We may have exaggerated a bit here but where might you find this type of combination of displays? Would the users have plenty of time to work out what the displays were telling them? How could you improve the layout or type of displays used?

 

 
 
 

 

 

A general design checklist for displays

  • What is the overall objective of the display?

  • What information is needed to support the objective?

  • What is important about the displayed information?

  • Is the information used directly with other information?

  • What type of technology will be used for the display (mechanical, electrical)?

  • What levels of details and accuracy are required for the displayed information?

  • How often will the information change?

  • Does the display need to be continuously monitored?

  • Is the display output directly influenced by operator input?

  • Under what environmental conditions will the display be used/viewed (lighting, noise, distance)?

  • What else will the operator be doing while viewing the displays?

  • What are the physical and cognitive characteristics of the operators?

  • With what other equipment will the display be housed/viewed?

  • What sort of errors are likely to be made by the operator? Does the design help to reduce them?

 

 

Displays FAQs

Q. What are the latest ergonomic developments related to aircraft cockpit design? Answer

 

Reference
Ergonomics: standards and guidelines for designers, 1987 British Standards Institution, London

Acknowledgments
Content: Mike Tainsh, Samia Abdi, Roger Harvey
Images: IMSI's MasterClips Collection