Guideline summary

Setting performance criteria

The selection of performance criteria should be defined in terms of mental activity. It should depend on the frequency of operator's activity :

Minimum psychomotoric activity, for frequently used actions, learned by practice . When applied to attention-consuming activities, a solution based on this criterion might result in operator's confusion, and mistakes.
Minimum attention capacity for occasional used actions, such as in exceptional situation , especially in emergency. When high speed human activity is required (such as in text editing), a solution based on this criterion might result in poor performance.

Setting the design focus

Skill development issues are relevant to routine operation , in which skill can and should be developed. Skill development is less important for most recovery procedures, which are rarely used. However, it may be applicable to recovery procedures that are used often (such as the Undo feature in word processing).

Consistent response to control activation

Whenever possible, the system response to an action should be consistent. This means that the operator's action should not depend on the context.

Avoiding context dependency

For routine operation, the dependency of the user actions on the context variables should be minimized;

Context visibility

Context variables should be based on primary visual cues (graphical information) to enable at-a-glance recognition, when consistency is impossible to achieve.