I suspect, as supplied, all the switch units respond to channel 1, thus when we set one at channel 3 for instance it still responds to channel 1. Great use as time switches for fish tanks, surprised more people don't use them....advantages as far as I am concerned are: - Can put 4 switched sockets next to each other on a 4 way extension block (unlike normal digital timers). - Can change on/off times of the devices from comfort of your arm chair. - Easy to move clock forward/backward for all switched sockets in spring/autumn at clock change time. - As you state, need to turn light on to have a morning inspection, no need to faff around in electrics cupboard to locate the timer override switch. Just press "on" and "off" when done.