Also, the TV didn't just send the currently-tuned channel 'down' the chain, it also allowed connected devices to inject their own, synced, video back into the TV, so you could be watching a show on BBC1, say, and the VCR could overlay a box in the top-right corner letting you know it had started a scheduled recording off Channel 4. Or, if you used a device like a Selectavision, if you tuned into a scrambled channel the Selectavision would notice, decode it, and send the descrambled version back up to the TV, all without the user realising it. Those clever Frenchies.