Well, let's throw in the Airbus trim: There are no trim switches like you see them on other planes. There are the trim wheels on the center console, but they are only used to set initial trim for take off, then you don't touch them unless a lot of stuff goes wrong and the airplane drops out of its normal law. When it does this, it goes into alternate law...no, still autotrim. Only when it goes to direct law, a message appears to use the man pitch trim, the wheels. So you fly with the stick and trim with the wheels. If it gets real bad, you go to mechanical backup. Now a red message tells you that all you have to control pitch is the trim wheel, the stick is dead. How does the plane know how to trim itself when autotrim is active? With the stick you tell the computer where you want the airplane to go (you give it a flight vector, a vector in space, to follow). If you set the nose 3 degrees up, the flight controls deflect as instructed by the FBW to maintain the resulting flight path, not just the attitude. With the given thrust, the airplane settles into the new direction and the system trims for a 1 g condition while following this vector.
That gives us a few funny things like trimming when down when you are in a constant rate climb and the plane enters an aera of updraft. The airplane is lifted and moves above the commanded flight vector. The FBW reacts by initially lowering the nose a tiny bit to return to the original vector to maintain. A conventional airplane would have just experienced an increased rate of climb , but previously in trim , it would have stayed in trim.