Alibi Clock

 
An alibi is the argument that a person was somewhere else or has to be somewhere else at a stated time. It is usually used in the context of a defence in a law court where the accused claims innocence on the grounds that other people can provide an alibi - i.e. support his case that he was somewhere else at the time the crime was committed.

An alibi clock was the name given to a striking clock that, because of an error in the setting of its mechanism, would show one hour on its clock face but chime a different hour.