 Because he only had a wiring schematic and not a signalling diagram he didn't appreciate that the starter signal was 'slotted' to four other track circuits, and was only supposed to clear once all those sections of line ahead were unoccupied.The effect of his actions meant that the signal would now revert to clear once a train had passed it by just 33 yards, rather than the 615 yards it was designed to.When he returned to the station he stood by the tunnel headwall with a red hand lamp and held every train for one minute after the signal turned green as a precautionary measure.