Tube signal

On my way home today, while waiting for a High Barnet tube train at Moorgate, I saw the platform attendant holding up his white bat to signal that the train could leave. This happens all over the tube network, and I’ve always wondered how the drivers can see the signal when they are buried in their carriages. So…I asked! It’s not magic, but it’s clever – the attendant is holding up the bat to a camera located halfway along the platform which transmits the image to a monitor inside the driver’s cab. Another mystery solved!