Sorry to disagree with you, Tony, but the knob you refer to marked D/R (Dual Rate) is exactly that. It allows you to quickly reduce the sensitivity of the rudder, by reducing the throw by an equal amount on either side of neutral. It is not an end-point adjuster, which would allow you to adjust the end point of either side separately.
I do accept the fact that for some purposes it might serve the purpose of an end-point adjuster. In my opinion, this radio is rather overpriced for what it is.
David.