From the instructions:

- The outdoor values and the channel number are shown on the display of the base station. If you have connected more than one external transmitter, you can switch between channels 1 to 3 with the CH/+ key on the base station.
- You can also set an automatic channel change.
- Press and hold the CH/+ key to activate the automatic channel change.
- Briefly press the CH/+ key to stop the automatic channel change and to have the desired outside station permanently displayed again.