Hi Somebody mentioned that the original question was...
What happens, with a plane like a PA28, trimmed for straight and level flight if the pilot:
1) Increases the engine rpm by 100rpm
2) after returning the plane to straight and level, trims the plane slightly up?
In both cases, if you were at say 2000ft S+L, the plane would try to find a new equilibrium altitude at say 5000ft and then would fly S+L there... Of course it would take a long time, the final levelling off would be at less than 100ft/min.
So you could say that the Trimmer ultimately controls the S+L Altitude.