How do I stop my gameobject from jerking and rotating on first touch

I use this code in rotating a gameobject by touch, immediately I touch the screen (on first touch) the gameobject jerks and rotate before my actual movement. How do I stop it from jerking. Note I use touch.move to call this in update

public void RotateMove() { zRotation -= Input.GetTouch(0).deltaPosition.y * rotateSpeed * invert * Time.deltaTime; // this limits the rotatioon zRotation = Mathf.Clamp(zRotation, -80, 80); //this rotates the game obj var eulerAngles = takenObj.transform.eulerAngles; eulerAngles.z = zRotation; takenObj.transform.eulerAngles = eulerAngles; }