This is the MK1 GTI campaign cluster.
The switch between 1 and 2 is the trip and total mode.
Mode 1 resets the MPG, average speed etc every time the engine is out for a few hours.
Mode 2 needs to be reset manually. Select either mode and then twist it a bit more in either directions and hold it there until the screen goes blank. It is now reset.
Use the button on the stalk to cycle between the screens.
There are also hidden menus that can be seen be keeping the button on the stalk pressed as you do this. Turn the key to the on position, off and then on again. Release the button and you are now in the hidden menus which display some usefull info like instant MPG, digital speedometer, digital tachometer and some other crap which are identifications for the year of the car, upper speed limit etc.