Looking at the side of the ECU you can see a yellow sticker and a little knob.

What does this actually do?

Is it set in the right position?

mines all the way anti clock wise,
I think its something to do with the idle mixture, but I'm not 100% on it,
all I was told by Stewart at SWR 15 old years ago when I did the conversion was "DON"T TOUCH IT"

Pretty sure it's a switch to put the ecu into diagnostics mode, I think all nissan ecu's run them , it makes lights flash on the dash like morse code and it gives you codes to tell ya whats wrong with your car

OK. I have had 2 different answers to this question. Is anyone 100% sure what the knob is for. I am guessing the knob is the fuel mixture but I am not sure. Could some please confirm what this is for.

its for diagnosis for the computer, most nissans have them, look at the vl and 31 skylines they are under the seat in them not too sure where they are in this either under the seat or in kick panel

some nisans have a harness that u bridge out for diagnostic mode and the ecu light flashes to get the fault codes

It doesn't make sense that a variable switch would be used to put the ecu into diagnostics mode.
What happens when you turn it half way, does it go half into diagnostics mode?
A simple switch would be used for this, not a variable switch.

It's more likely to adjust mixture.