A self-checking process where no action is required by the SignallerA person responsible for the operation of the Signalling System, to safely control the passage and regulation of trains, usually located in a Signal Box. or
engineer, which ensures correspondenceThe agreement of the Interlocking with the Detected state of a Signalling Function. between the Signalling SystemA series of electrical, electronic, electro-mechanical units brought together to form a system which controls the safe movement of trains.
and the actual state of the railway.