Types of user controls
- Computer keyboard in text editing. The outcome of pressing many of the keys depends on the Caps Lock, Num Lock and Overwrite modes.
- Buttons on a TV Remote control. The outcome of turning on-off, resetting and scrolling applies to the selected source, which might not be the one that the user intended.
- The effect of the steering wheel on the rudder of the Torrey Canyon was depended on the position of the steering control lever for the autopilot.
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.  Such failures result in negative feedback, which hampers skill acquisition. Occasionally, such failures result in accidents. 
The outcome is independent of any of the system variables. These controls are those that support direct mapping from intentions to actions. Examples:
- Top row (as opposed to the numeric pad) numeric keys in text editing
- Two-state switches, such as power-on/ off and light control
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.
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.
- , Harel & Weiss, Mitigating the Risks of Unexpected Events by Systems Engineering
- , Zonnenshain & Harel: Task-oriented SE, INCOSE 2009 Conference, Singapore