The turnstile state machine can also be represented by a directed graph called a state diagram "(above)". Each state is represented by a node ("circle"). Edges ("arrows") show the transitions from one state to another. Each arrow is labeled with the input that triggers that transition. An input that doesn't cause a change of state (such as a coin input in the Unlocked state) is represented by a circular arrow returning to the original state. The arrow into the Locked node from the black dot indicates it is the initial state.