Revs
Gear, revs, speed and shift lights
What it is for
There's no time to read a rev counter on the way out of a corner. The lights come on one by one as the revs climb and flash when it's time to shift — your eyes stay on the track.
It helps most when you can't see the dash: the wheel hides it, or your field of view is too narrow. Gear and speed are still right in front of you.
Where you change it
Each change takes effect at once — there is no apply button.