You can also adjust the level of the instrument lighting with the same button.
'm not sure the instructions for this are in the manual so, with thanks to Planenut, here's his post from 2012:
The backlight level can be accessed as follows: Turn on the ignition, press the indicator button until voltage is shown, press and hold it until "ILL" is shown then press it quickly so it cycles through the different levels (lights on) between 1 and 10. You can set the level with another long press of the indicator button. Other than maybe messing the clock time up I don't think there is anything that will "end the world" in the secondary menu but I could be wrong! Good luck
