The signals used on the Great Northern to work the block system were lower quadrant semaphores. A lever in the signal box was connected by a wire (under tension, and passing over intermediate pulleys) to a counterweighted arm on the signal. To set a signal to all clear, the signalman pulled the appropriate lever in his signal box; this moved the arm down (which was pivoted in a slot in the signal post), against the pull of the counterweight, "to a vertical position in the post". When the lever was moved to set the signal to danger, this did not positively drive the signal to “danger” but paid out slack in the wire and allowed the counterweight to take the arm to a horizontal position.