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Constraints (Physical (More effective if the constraint is easily…

- - - - Existing standard is kept even though new standard might resolve problem
        
        Difficult to change equipment/products to fit new standard
  - - - Malfunction at one stage prevents the next step from being taken place
    - - Interlocks
        
        Forces an operation to follow a prescribed sequence
        
        Examples
        
        Dead man's switch
        
        Park brake can only be released if brake pedal is depressed
      - Lock-Ins
        
        Keeps an operation active to prevent its stoppage
        
        Example: Dialog box to verify Exit without saving on PC applications
        
        Literal
        
        Virtual #
        
        Manufactures use this feature to ensure product loyalty
      - Lockouts
        
        Prevents an action until desired operations have been completed
        
        Mainly used for safety
        
        Examples: Baby locks and gates, cover for electrical outlets, childproof caps on Rx bottles
        
        Nuisance in normal usage
        
        Many people disable
        
        Designers can make use of a forcing function to assist in another manner
- - - - Universal conventions have not been agreed upon
  - - - Schank and Abelson suggest we follow cultural "scripts" that guide our sequence of behavior
  - - - When conventions are violated; new learning is needed
        
        Change of a new system can be upsetting