Ignition Switch

Often a physical machine is modeled as a finite-state automaton. The state transitions correspond to actions performed on (or by) the machine. The diagram shows an automaton that models the ignition switch of an automobile.

The switch starts out locked. Inserting the key corresponds to the state transition from "locked" to "off". Rotating the switch right moves the switch to the "accessory" position. Further turning the key brings it to the "on" position (although the motor is not yet running). A further right turn and the starter motor is engaged in the "crank" position. (It would be awkward to call this the "start" state).

In this automaton the symbols labeling the state transitions are not single characters. This is only a small change. The symbols could just as easily be 'I' (for insert), 'R' (for right), 'L' (for left), and 'V' (for remove).