7.3.4-3 Visibility of Interlocks, Lockouts, and Lockins

Interlocks, lockouts, and lockins should be designed to indicate which actions are being blocked and what conditions activated the block.

Additional Information:
A lockout blocks inputs that it considers unacceptable or not achievable. When this occurs, the user should be able to determine why an input was blocked and what inputs are acceptable, especially for context-sensitive validation in which complicated rules may be used for assessing the acceptability of an input value. An interlock should inform the user of the condition(s) that activated it and the conditions that must be satisfied to release it. Lockin features should show the user what action is being 'locked in' (i.e., the action that is being caused to operate without interruptions) and how it can be canceled.