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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!
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Effective
visual displays
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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.
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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:
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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.
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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.
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Classification
according to type of information displayed: |
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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.
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? ? ? ? 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.
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?
? ? ? ?
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. |
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Design guidelines for displays
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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.
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Illumination
Displays may have their own internal or back-lighting, but if not, their design should be suited to the lowest expected
lighting level.
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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.
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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.
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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.
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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.
 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.)
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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.
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Display
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?
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 A general design checklist for displays
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What is the overall objective of the
display?
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What information is needed to support the objective?
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What is important about the displayed information?
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Is the information used directly with other information?
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What
type of technology will be used for the display (mechanical,
electrical)?
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What levels of details and accuracy are required for the displayed information?
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How often will the information change?
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Does the display need to be continuously monitored?
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Is the display output directly influenced by operator input?
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Under what environmental conditions will the display be
used/viewed (lighting, noise, distance)?
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What else will the operator be doing while viewing the displays?
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What are the physical and cognitive characteristics of the operators?
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With what other equipment will the
display be housed/viewed?
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What
sort of errors are likely to be made by the operator? Does the
design help to reduce them?
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Displays
FAQs
Q. What are the latest
ergonomic developments related to aircraft cockpit design? Answer |
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