1.3 Ensure that controls are adequately sized and sufficiently spaced to be operated by people with limited dexterity
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 that the user does not accidentally activate two at once.
Many, particularly older, users have reduced dexterity in their hands due to degenerative conditions that affect their muscle control or that cause uncontrolled movements such as shaking. Small controls can be difficult to operate for these users because they either cannot accurately target them or because 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.
Make boundaries between controls clear
Clearly define the edges of buttons and keys using a ridged border which is darker or lighter than the control itself.
Space controls sufficiently
Leave a gap of at least 2.5mm between the edges of adjacent buttons or keys.
Shape the input slots
Design a funnel-shaped entry to the card input slot or other slots, to help guide the items in.
Avoid difficult physical actions
Avoid operations that require more difficult physical actions such as fine positioning of rotary controls or time-limited actions such as double clicks.
Present enough of the output for the user to grasp
Ensure that outputs such as tickets, money or receipts protrude at least 2cm from the slot surround.
Allow user-selectable settings
Applying the previous techniques should result in a terminal which 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, if the terminal uses a touchscreen, there is scope for offering alternative layouts of controls. Users with limited dexterity could choose a layout using large, widely spaced controls spread across two screens, whilst users with good dexterity could choose a more detailed layout in which everything is included on a single screen.
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.
Self-test early prototypes
Designers can run simple tests on an early prototype, although it is difficult to properly simulate low dexterity. One possible method is to try operating the prototype using a finger-shaped pointing stick rather than with your fingers. Because it will be more difficult to be accurate, you may get some idea if major problems are likely to occur. Another possibility is to try operating it while wearing workshop gloves. It would be possible to simulate a hand tremor by shaking the user's hand or arm or by shaking the prototype. However, you should take extreme care in doing either of these since both could be highly dangerous.
Test with real users
During development, you should test the prototype in a realistic situation with real people, particularly older people.
About user testing