Users will normally access the functions of the terminal through controls such as buttons, keys and knobs. These may or may not be visible to users who are blind, partially sighted or colour blind. However, all users with restricted vision must still be able to use all the functions. Where possible, the controls should be designed so that at least users who have partial vision or colour blindness are able to perceive them, understand what each is for and know how to operate them. It may also be possible to design the terminal in such a way that users who are completely blind can still perceive, distinguish and operate the same controls. If this is not possible or extremely difficult, an alternative control method should be made available, which these users can perceive and can be used to access the full functionality.


Keys should be well spaced, tactilely discernable and contrast visually with their surround.

The user should be able to operate any control, such as a button, key or knob, without accidentally operating any other control at the same time. This means that each control should be sufficiently large for the user to target and activate it, even if they suffer from limited dexterity through lack of motor control or shaking hands. Precise activation should be possible even with shaking hands. Controls should also be sufficiently spaced out so that the user does not accidentally activate two at once.

A uniform presentation and interaction style should be used for all functions of the terminal. This should not change between visits.

The steps required to complete a task should also remain the same between visits. This includes the instructions, the choices provided, what inputs are required and how these are made.

Having completed one task, the user should be able to complete a second task by carrying out a similar sequence of steps. Having carried out a task once, the user should be able to return to the terminal at some later time and repeat the task by carrying out the same steps.

If a service is delivered through a number of different terminals, they should use a similar presentation and interaction style. The layout of controls and keypads and the location and orientation of slots or dispensers for cards, money, tickets or receipts should be the same on each version of the terminal.

Having completed a task on one terminal, the user should be able to complete the same task on a different terminal by carrying out a similar sequence of steps.


Certain controls are more applicable to some tasks than other controls - the best design depends on the demands of the task. The following features should be considered during the design stage:

  • The ease of discrimination of individual controls;
  • The arrangement for operational use;
  • The spacing of controls;
  • Multiple modalities;
  • The use of colour;
  • The use of icons and labels;
  • Consistency.

Ease of Discrimination

Salient features will be most noticeable in situations where only a short time is available to deduce control information. Creating distinct controls would enable sighted and partially sighted people to find controls quickly. Discriminability is paramount because people spend longer discriminating between features that are similar than those that are radically different. Obviously, as the size of a control increases, the easier it is to see it and the easier it is to locate it because it would occupy more space.

Size is often assumed to be an indication of importance, with larger items being displayed superior to smaller ones. A bright saturated colour amidst a dull array of controls will be very noticeable. But the same control placed amongst other colourful controls will not stand out in the same way. Arrays that are symmetrical are more aesthetically pleasing but can become monotonous. Asymmetrical arrays (which are characterised as having more visual weight on one side of the central axis than on the other) are interpreted as being more informal.

If a lot of controls are presented together but not easily recognisable or grouped in a comprehensible way, the user's fingers can get lost amongst the array. Distinct features identifiable by shape, size etc. Can be used as reference anchor points for the fingers or palm to facilitate finding specific controls.

Distinguishing features of various controls can be used to create a starting place from which other functions can be easily found or can be designed to be used in this manner, similar to tactile maps. Tactile maps use symbols to indicate specific locators.

Blind positioning movement involves reaching for a control when the person's eyes are busy. Research into this area reveals that it is most accurate when the controls are placed straight in front of the person. The accuracy of reaching for controls decreases the further to either side they are placed. People tend to be more sensitive to differences in location vertically as opposed to horizontally. So the spacing between controls should be greater in a horizontal direction. Controls located between waist and shoulder height are more accurately found than those above head height. Optimally, controls should be placed straight ahead and at or below shoulder level.


Devices are easier to use when the controls are placed in a logical manner. Some principles for control arrangement are:

  • Frequency of use - controls that are used frequently should be placed in a convenient location, if appropriate, between elbow and shoulder height. This is useful for complicated systems where they are numerous functions;
  • Importance principle - important controls should be located in a convenient place;
  • Sequence of use - the layout should reflect the sequence of operation. This is useful for simple systems. For example, horizontally, the first button to use is placed at the far left, the second is placed to the right of that and so on. Visually impaired people find it easier to read from left to right rather than in columns or right to left;
  • Functional grouping principle - places closely related functions next to one another whilst making them easily and clearly identifiable. These could share spatial, physical or temporal attributes. Groups can be distinguished by spacing, colour, shape, size and boundary borders;
  • Colocation - this relates to the compatibility of displays and their controls. The layout of the controls should reflect their displays so their relationship is evident;
  • Consistency principle - the layout with the shape components located in the same spatial location would minimise memory and search requirements. Using consistent labels and messages will reduce the risk of creating errors.

Some principles are more powerful e.g. Sequence of use and functional grouping principles. Any of these principles may conflICT so discernment is required when applying these principles to a specific design.

Controls that are rarely used but are required on the console could be positioned under a hidden panel so they are still accessible but do not clutter the important functions.

Spacing and Size

With greater space between controls, inadvertent operation errors decrease but performance is also affected. If controls are placed too far apart, they will require a lot of movement which could become tiring over time. If controls are placed too close together, inadvertent operation of more than one control is possible. Errors of touching other controls are greatest for knobs to the right of the one to be operated and least for the controls to the left.

Crowding controls together decreases the amount of "white space" around them, creates spatial tension and inhibits scanning. It can also produce distracting effects when lines are too close.

When control area space is at a premium, smaller diameter controls result in less errors whilst maintaining performance. For different control configurations, the optimum size of clustering would need to be tested.

Many, particularly older, users have reduced dexterity in their hands due to degenerative conditions that affect their muscle control or cause uncontrolled movements such as shaking. Small controls can be difficult to operate for these users because either they cannot accurately target them or the uncontrolled movements cause their hands to stray off them. This makes the terminal difficult to use. In extreme cases, the user may accidentally strike the wrong button or key or strike two at the same time, causing errors. This can be particularly problematic with touchscreens or contact-sensitive controls where the user's hand may wander over the wrong area. The problem is made worse by the controls being closely spaced. Another problem may occur if controls require finely controlled activation or positioning, such as double-clicking or precise positioning of a rotary control.


Designing for more than one sense modality is preferred because people vary widely in their capabilities and it helps compensate for overloading of one or more senses. Control identification is created through coding the controls size, shape, texture, colour, location, labels and operation method. Which of these factors are relevant and their parameters depend on the detectability, discriminability, compatibility, meaningfulness and standardisation of the codes. Incorporating more than one sense into a design can compensate for a sensory channel that has been adversely affected e.g. In a cold environment, peoples' tactile sensitivity is lessened and wearing gloves will also decrease this. People with diabetes may have decreased tactile sensitivity.

Tactile sensitivity is essential to discriminate shapes of controls, especially when vision can not be used. This is helpful to everyone, especially in darkened environments. Basic forms like round shapes are memorable, simple and pleasing to the eye. Military research has designed controls so they are not often confused with one another. If these shapes are related to the control's function, they are even easier to correlate and remember. This symbolic association is used in cockpit design and could enable blind people to identify controls.


Colour can be informative when used to link information as long as it is used in moderation. It does this by linking elements together to indicate organisation and relationships. Colour helps in searching tasks by drawing attention.

Optimally 2-4 colours should be used. But colour can be distracting if overused so only colour a few items. Also, users must look at a colour to be able to identify it. Red can be associated with "stop" or "danger" but a significant proportion of the male population in the UK is red/green colour blind. Some people with retinitis pigmentosa may have difficulties reading a red display. A lesser proportion of the population is blue/yellow colour blind. Colours used should not cause adverse visual after effects. Colour coding should not cause problems during the night. Poor illumination, dirt or lack of vision can obscure this form of coding but combining colour with another coding method can increase discriminability.

Icons and Labels

Icons used on buttons and controls must be easy to understand. Currently the "enter" button on most keypads uses a "return" arrow which is left over from the old-style typewriters where this icon indicated a "carriage return"; the meaning is not obvious unless the user is old enough to remember moving carriage typewriters. In many cases, it would be better to use the appropriate words rather than leave the user to guess the meaning of the icons.

It is important to keep icons as distinct and simple as possible. They should provide enough information to convey the message because too much information causes people to take longer to recognise them.

Control labels, prompts and delivered information are usually provided as text but presented visually. Any user who cannot see to read the text will not be able to perceive the information it contains. The controls themselves have first to be perceived by the user before they can be operated. Again, this often relies on sight, so people with restricted sight may be unable to use the terminal. A particular problem occurs with terminals that use unlabelled buttons for input, changing the prompt next to each button on successive screens. Knowing which button to press relies on visible correlations that are difficult to learn.


People with cognitive or learning disabilities find it difficult when the presentation, interaction style or task flow varies. Consistency helps enormously by making procedures easier to understand and enabling users to transfer the skills learnt on one task to other tasks. If there is no consistency between tasks or, even worse, if there is no consistency over time for a given task, users will have to repeatedly relearn the procedure.

Consistency is also vitally important for users who have difficulty perceiving the instructions and controls. Memorising a routine sequence of button presses to withdraw cash is the main strategy employed by blind ATM users. If the interface changes at all, for example by the addition of advertising messages or unexpected questions into the screen flow, their standard sequence of steps may fail.

People with cognitive or learning disabilities find it difficult when the presentation, interaction style or task flow varies. If there is no consistency between different terminals, users will have to repeatedly relearn the procedure.

Consistency is also vitally important for users who have difficulty perceiving the instructions and controls. Memorising a routine sequence of button presses to withdraw cash is the main strategy employed by blind ATM users. If the position of buttons is different from one terminal to another, their standard sequence is of no use to them.

Directions and Techniques

It is standard practice to put a single raised dot on the 5 key to help users orientate their fingers on the keypad by touch. It is also possible to emboss Braille on keys and buttons, although this is not as widely effective as it may seem since less than 2% of visually impaired people can read Braille. Also, Braille has less value in outdoor situations during cold weather because tactual sensitivity is dramatically reduced at lower temperatures.>Raise or recess the buttons and keys by at least 2mm over the surrounding area.

remote control

Make buttons large and tactilely discernable.

Provide tactile and audio feedback to indicate the operation of controls. Tactile indication can be provided by requiring a gradual increase in the force to activate a control, followed by a sharp decrease as it is activated. Audio feedback can be given using a beep or click. For multiposition controls, feedback should be used to indicate the current position or status.

Ideally, keys should be internally illuminated when the terminal is waiting for input from the keypad.

For label text, ensure that characters are at least 4mm high but avoid using all upper case which is more difficult to read than mixed case. For good contrast, use light coloured characters on a dark background, e.g. White or yellow on matt black or a dark colour. Avoid using pale colours or patterned backgrounds for text. Also avoid red on green or yellow on blue since these combinations may cause problems for people who are colour blind. Use a typeface designed for display, such as Tiresias, which has numerals with open shapes that are easier to distinguish for people with low vision.

Whilst colour coding can be useful as an aid to recognition, it should not be relied on entirely since more than 8% of Irish males and some females have difficulty distinguishing between red and green (other forms of colour blindness are relatively uncommon).

Applying the previous techniques should result in a terminal that suits all users. However, in some cases, what is best for one group of users is not necessarily best for all. If this is the case, it may help if the user interface can be adapted by the user, or automatically for the user, to fit their individual capabilities. For example, users who are visually impaired could choose voice output and large type, whilst users with good vision may prefer to have more detail and no sound. The choice could be made by the user selecting from a number of displayed options. Alternatively, information required for the terminal to switch automatically could be encoded on a user's smart card at their request.

The telephone layout is recommended as the standard for public access terminals. Using this layout will ensure the most consistency with other terminals.

numbers layout

Use telephone layout for keypads.

Clearly define the edges of buttons and keys using a ridged border that is darker or lighter than the control itself.

Leave a gap of at least 2.5mm between the edges of adjacent buttons or keys.

Make buttons large and tactually discernable.

The standards in various countries differ over the embossed symbols to be used on the function keys. The most prevalent are: Cancel "X", Clear "I" or "<" and Enter "O".

embossed symbols

Typical example of the embossed symbols used on function keys.

Controls and keys should be tactually discernible without activating the control or keys. The status of all locking or toggle controls or keys should be visually discernible and discernible through either touch or sound.

Avoid operations that require more difficult physical actions such as fine positioning of rotary controls or time-limited actions such as double clicks.

Applying the previous techniques should result in a terminal that suits all users. However, in some cases, what is best for one group of users is not necessarily best for all.

The sides of the privacy shield can be angled inwards to give more room around the keypad, but this increases the total area taken up by the keypad. A possible alternative is to have a removable (e.g. Hinged) privacy shield for people who have problems in using the keypad when the shield is in place. However, this may be difficult to make vandal resistant and it may be difficult to discourage users from removing the shield.

How you could check for this

Designers can run simple sight tests on an early prototype by simulating various types of vision loss. Complete loss of sight can be simulated by wearing a blindfold, turning off the lights or concealing the terminal in a bag. To simulate partial sight, a test user who normally wears glasses could take them off. It is also possible to buy low vision simulation glasses that simulate various types of visual impairments.

In all cases, extreme care should be taken to avoid injury through loss of balance or collision with unseen objects. This may require that the test user remains seated or, if they have to move around, obstacles such as floor cabling are removed in advance. Although this type of ad hoc testing will not replace proper testing with real users, it will give some insight into what it is like to be operating with reduced vision.

Where possible, follow simulation testing with testing by representatives of user groups in realistic situations.

During testing, the following key checks should be made:

  • An adjustable privacy shield should be provided;
  • Provide a consistent user interface for similar terminals;
  • Ensure tactual differentiation of keys;
  • Use appropriate colour coding;
  • Ensure tactual markings on function keys;