It adjusts the pitch curve in idle up. If it is all the way counter clockwise, then you will have 50% throttle in idle up at mid stick, and if you have it all the way clockwise, then it will be 100% throttle at mid stick. If the knob is half way it will be 75% throttle at midstick in idle up. Alwyas of course at the 0 stick and full stick in idle up the throttle will be 100%