Exactly what is differential in the control surface?Is that the difference in degree of setting from normal or what?

Differential is when the ailerons move a different amount up than down. The down moving aileron tends to cause more drag than the up moving aileron which ends up counteracting the turn command to some degree. This is mainly an issue in high-wing planes, like cubs. By programming the ailerons such that they go down only about 2/3s as much as they go up, this issue is reduced or eliminated and the plane responds to the turn command more smoothly.

Thank You RBACONS.I was thinking about getting a AXN cloud floater that's why I asked!��

Here's a link that should help you understand What the purpose of differential is: http://www.rcflightschool.com/Basic_...lo_0B16-25.pdf

The down moving aileron makes more lift. More lift is more drag. More drag pulls that side back.

The up moving aileron decreases the lift on that side. Less lift is less drag. That side moves forward while the other is pulling back.

Rolling into a turn is more efficient. Yet, as you can see, those ailerons yaw the plane the other way. Not good.

The longer the wing, the more leverage the ailerons have. So sail planes usually have problems that go unnoticed in the average power model, like Ugly Stiks and such. Any wing with dihedral winds up fighting itself. Another reason gliders or floaters benefit from differential.