ORIGINAL: MikeEast
For Example, and this is just a basic non technical explaination. With an analog servo, if you pull back on the elevator to full up elevator an analog servo sees a signal to move. It puts out a given amount of current and the shaft rotates. It does not care how much or how many degrees the servo shaft rotates or what the deflection of the servo arm is, its just deals out a certain amount of "power" basis your stick input. So if you are flying and the wind pushes back on the surface the current to the servo does not change and the servo gets "pushed back". It may rotate 30 degrees on the ground and only 29, or 28 or 25 degrees depending on headwind and how fast you are going. A digital servo in the same situation will increase power to hold the position of the shaft and thus the servo arm which means the control surface does not get pushed back.
What? How can that be?
I have both digital and analog servos on many planes.
If I turn on my plane and radio, it centers the analog servos.
Then if I manually push on any surface to change the position of the control surface, thereby moving the analog servo...
IT MOVES RIGHT BACK TO CENTER.
Likewise if I hold it at a particular position and move the surface, it goes right back to that position.
As soon as there is any force moving the control surface away from the commanded servo position, the analog servo starts pushing the surface back to where it was.
The servo want to go back to a particular position.
That doesn't correspond to the above.
I've purchased several planes that while they call for digital servos, but could do just as well with a good set of high torque servos.
For average sport fliers there are many times when the extra cost of the digitals is not needed.