Delta touch trembling

hello!

Quick question guys, I use the delta mouse position (or delta touch on device) to raycast on a Plane so I can get accurate camera movement that follows the finger. this works fine, however on device there is a lot of trembling if I keep my finger quite static on screen. it seems like the accuracy is not enough with the raycast. I tried a SphereCast and a CapsuleCast with various radii but they didn't help much. it keeps trembling!

This is part of the code:

 if (Input.GetMouseButtonDown(0)) {
 
     currentTouchPos = currentTouchPos = Input.mousePosition;
 
     getPointOnPlane (currentTouchPos, out initialTouchPos);
 
 }
 else if (Input.GetMouseButton(0)) {
     previousTouchPos = currentTouchPos;
     currentTouchPos = Input.mousePosition;
 
     currentTouchDelta = findAccurateDeltaPos(currentTouchPos);
 
         panning = true;
 }
 
 private bool getPointOnPlane (Vector3 touchPos, out Vector3 point) {
         if (plane.Raycast (ray, out f)) {
           point = ray.GetPoint (f);
 
           return true;
          }
 
       return false;
 }
 
 private Vector3 findAccurateDeltaPos(Vector3 touchPos) {
 
     Vector3 pos = Vector3.zero;
     if (getPointOnPlane (touchPos, out pos)) {
 
         Vector3 d = (initialTouchPos - pos);
         return d;
     }
 
     return Vector3.zero;
 }

I then simply move the camera by the "currentTouchDelta", which is the world-space delta position, calculated in the findAccurateDeltaPos method. Any ideas?

Thanks a lot