2.2 Ensure that the user interface and task flow is similar across different functions

Rationale

All users find it difficult when the presentation, interaction style or task flow varies. People with cognitive or learning disabilities find it particularly difficult. 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. The consistent placement of interface elements from one screen or dialog to another makes it far easier for screen magnifier and screen reader users to find things. Memorising a routine sequence of actions is a major strategy employed by blind computer users. If the interface is inconsistent so that the task flow varies from function to function, they will be less able to use standard sequences of steps.

Directions and Techniques

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. Standards 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 a quality assurance role, reviewing the design to ensure it adheres to the style guide. It may be possible to enforce the standard automatically, by developers using templates or some kind of content management system.

How you could check for this:

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.