User control

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Systems are operated by controls, such as buttons, mice, switches, levers, dials, etc.

Types of user controls[edit]

State-dependent controls[edit]

The outcome depends on a system variable, typically, a system state. Examples:

The users need to be aware of the system state during the operation of these controls. Failure to notice an unintentional state change results in undesired results. [1] Such failures result in negative feedback, which hampers skill acquisition. Occasionally, such failures result in accidents. [2]

State-independent controls[edit]

The outcome is independent of any of the system variables. These controls are those that support direct mapping from intentions to actions. Examples:

State independent controls are easy to use, because their effect is consistent: a state-independent control actuates a unique function, which is independent of the history of previous activity: the user does not need to check and verify the system state, or to consider the possible outcome. State independent controls are easy to learn, because they are not error prone. They enable carefree operation.

Value-adjustment controls[edit]

These are controls used to set a value of a continuous variable, such as of analog devices. Examples:

  • Analog controls, used to control dynamic systems, such as steering,
  • Setting the cursor on a computer screen using a mouse,
  • Volume control of a TV system or a telephone,
  • Threshold setting of sensors, such as in warning systems.

Value-adjustment controls are easy to use, because the user is in the loop, focusing on a single parameter, evaluating the effect of the current setting and getting direct feedback about the effect on the setting.


  1. ^ [1], Harel & Weiss, Mitigating the Risks of Unexpected Events by Systems Engineering
  2. ^ [2], Zonnenshain & Harel: Task-oriented SE, INCOSE 2009 Conference, Singapore

External links[edit]