In a TV - DVD recorder - Set top box configuration use the 'TV/DVD' switch to switch back and forth between Set top box reception and DVD recorder reception.
This only functions when you used a Scart cable to connect the DVD recorder to your TV set and if your TV set responds to this switch-over. This function is useful
when, for example, you want to watch a channel from the Set top box on your TV and make at the same time a recording from another source.