7.3.7-1 No Activation When Display Is Inoperable

Users should not be able to activate a soft control if its display is not working.

Additional Information:
A reported problem with touch screens is that sometimes their buttons may remain active even though the video image is not visible. Thus, a user could touch a blank screen and provide a valid input. Such problems may be avoided by requiring multiple actions, such as separate selection and activation steps, for inputs that may have serious consequences (e.g., affect the operation of plant equipment).