A Gauge is an abstract interactive object representing stateful interactive devices. One example of a Gauge is the Slider which maintains a value between the maximum and minimum value. The Gauge may change its state either discretely or `continuously' (continuously in the sense that listeners can see how the transitory values the Gauge goes through to reach a new state). For the Slider, a discrete change represents the warp of the slider thumb to a new position, `continuous' change would be the dragging of the thumb to a new position.
The Gauge abstracts away from the details of the user interface, defining a communication abstraction that captures the semantic and interactive behaviour of many common user interface components: