2.3 Ensure that the user interface and task flow is similar across different functions and remains the same across repeated visits
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.
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.
" I recently ran into problems with the ATM because the format had changed and while I was used to the position of the messages and could hit the right button to get my money out, when they changed the position I couldn't read the message and was foxed. " - blind bank customer
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.
Define and follow a standard style
Consistency is achieved by defining a standard style and following it. This can outline standards for aspects such as colours, control sizes, positioning, task order and writing style for instructions and information. It should be written down in the form of a style guide and one or more members of the development team should be assigned to act in an editorial role, reviewing the design to ensure it adheres to the style guide. It may be possible to enforce the standard automatically, by using templates or some kind of content management system.
Don't insert extra steps into a process
Avoid inserting extra steps into the sequence, such as advertising or promotion messages.
Try to repeat a task by using a standard sequence of operations
While carrying out a task, write down the sequence of operations you perform, in terms of physical actions such as button presses. Try to repeat the task a number of times by following this sequence exactly, without looking at the displayed instructions. If the result is in any way different, then there is inconsistency.