RE: Expotential??????
Expo is just as the name suggests. The servo moves "exponentially" with the stick. It is mainly used to make the Tx sticks less sensitive around the neutral points.
Without Expo, when you move the aileron stick 25% of it's travel, the servo will move 25% of it's travel. With Expo, when the stick is moved that same 25%, the servo will only move say, 10% of it's travel. As you move the stick to full travel, the servo still moves to it's full travel. Make sense?
Doug