Summary: This has a twist knob, which can be twisted or pulled, exhibiting a more complex example of bounce-back transitions. The device has a natural inverse in that twists in opposite directions do opposite things. In addition, the link between the knob and its logical state (volume and track selection) is time dependent, thus showing a different, but common form of linkage
This example is the controller of an old Sony MiniDisc player. The player itself would be put in your pocket, and the controller could be clipped onto your clothes while you walked or ran.
Although MiniDiscs were a short-lived phenomenon, the logical actions controlled by this device are similar to any MP3 player, or the music application on a smartphone.
As you can see, the controller had multiple buttons for things such as pausing the music and different playback modes. However, we will focus on the knob at the end that controlled the volume and track selection.
The knob could be twisted and this controlled the volume. Twisting clockwise increased the volume and anti-clockwise turned it down. However, it could also be pulled out, and in this position it controlled the selected track, moving the MiniDisc onwards or back.
The physigram therefore consists of a number of bounce-back transitions on the same controller.
As you can see, there is only one non-transient state – in the middle with the knob in. If you twisted from the central position, whether out or in, it always tried to bring you back, and while the knob was out it always tried to spring back in.
The position of the knob did not correspond to a particular volume or track, otherwise the bounce-back would have always meant it was in a medium volume on the middle track! That is, it is a hidden state device. However, given you would be operating the control by touch, being able to see the state of the system from the state of the knob was not critical. Furthermore, a fixed set of positions for track selection would have limited how many tracks were possible.
One way to use a device such as this to control a potentially unbounded number of tracks would be to repeatedly give it little twists to switch tracks up or down. Indeed, the device could be used in this way. However, like an autorepeat on a keyboard, if you kept the knob twisted for a certain period it would start moving through the tracks one by one of its own accord. In other words, there was a timed transition. There was the danger that you might overshoot, missing the desired track or volume. However, if you did you could simply twist in the opposite direction to reverse the unintended action; that is, the device exhibits a natural inverse.
In the following diagram, the physigram on the right is connected to the logical state of the track using named events (up) and (down). These events may be triggered by the initial user action, but also if the knob stays in the same off-centre position for more than a set period there is an event on a self-transition (no physical change) denoted by τ.
