Consistency is about the way the operators perceive the machine behavior: its appearance, and the way it responds to the operators' controls. It implies that the system response should always be the same, independent of the situation, system variables, or setup parameters.
Consistency enables high-performance user operation, due to mental automation. Because the system response to a user action is always the same, the users do not need to examine the system situation before deciding whether to invoke the action.
Consistency implies that users cannot change the system behavior when it does not match their needs.
Updated on 13 Jul 2016.