English: Transition diagram for a finite state machine modeling a turnstile, a common introductory example used to explain state machines. The turnstile has two states, Locked and Unlocked. There are two inputs effecting the state: depositing a coin in the turnstile, coin, and pushing on the turnstile's bar, push. The turnstile bar is initially locked, and pushing on it has no effect. Putting a coin in changes the state to Unlocked unlocking the bar so it can turn. A customer pushing through the turnstile changes the state back to Locked so additional customers can't get through until another coin is deposited. The arrow into the Locked node from the black dot indicates it is the initial state.