Mouse slingshot to touch control problem

I have a beautiful script adapted from a sidescrollling GUI script that lets me make a FPS slingshot GUI which has rotation control and adjusts tension according to how far you pull the finger away. It works beautifully on the computer but on touchscreen I have the much documented (Touch)MouseOrbit problem with some problem ( that I cant quite put my finger on) between the last finger touch and the new finger touch. A previous answerer suggested that I should look at .: .......TouchPhase.Began....... Then move it only in TouchPhase.Moved or Stationary with Quaternion.Lerp(...)

but i cannot think hot to implement it.... hope someone can help... here is my script....:

 #pragma strict
 var loadedobject : GameObject;
 var barHeight : int = 32;
 var TargetBack : GUIStyle;
  var projectile : Rigidbody;
 var spacer : int = 8;
 var catapault : GameObject;
 var tiles : Tile[]; // home-made class. see the end of script.
 var springSpeed : float = 5.0; 
 var throwSpeed : float = 8.0;
 var strengthx : float;
 var strengthy : float;
 var strength : float;
 var ThrowAngle : float;
 var loaded : boolean;
 var tension : float;
 var sling : GameObject;
 var spawnpoint : GameObject;
 var tester : GUIStyle;
 
 var tileSize : float;
 private var screenWidth : int = Screen.width;
 private var screenHeight : int = Screen.height;
 private var slidePosition : Vector3;
 private var maxSlidePosition : Vector3;
 private var oldMousePosition : Vector3;
 private var throwPosition : Vector3;
 
 
 function Start () {
     // in a real senario maybe this is dynamically created from a database. for now, here are some blanks.
     tiles = [new Tile()];
     oldMousePosition = Input.mousePosition;
    
 
 
     
 
     
 }
 function Update () {
     catapault.transform.rotation.x=0;
     catapault.transform.rotation.z=0;
     if (!Input.anyKey) {
       
                slidePosition = Vector2.Lerp(slidePosition, Vector2((Screen.width/2)-tileSize/2,Screen.height/1.5), Time.deltaTime * springSpeed);
             oldMousePosition = Input.mousePosition;
             
     }
 
 
 
     if((Input.GetMouseButton(0))&&(new Rect(Screen.width/3,0,Screen.width/3,Screen.height/2).Contains(Input.mousePosition)))
     
          {
         slidePosition.x += Input.mousePosition.x - oldMousePosition.x;
         slidePosition.y += (Input.mousePosition.y - oldMousePosition.y)*-1;
         oldMousePosition = Input.mousePosition;
        }
     
     
     else if((Input.GetMouseButtonUp(0))&&(new Rect(0,0,Screen.width,Screen.height/3).Contains(Input.mousePosition))){
         Missile();
 slidePosition = Vector2.Lerp(slidePosition, Vector2((Screen.width/2)-tileSize/2,Screen.height/1.5), Time.deltaTime * springSpeed);
         
         
         
         
         }
         
     if(slidePosition.x<Screen.width/2-tileSize/2){
     strengthx = Screen.width/2-slidePosition.x-tileSize/2;
     ThrowAngle=strengthx/strengthy*-1;}
     else {
         strengthx = slidePosition.x-Screen.width/2+tileSize/2;
         ThrowAngle=strengthx/strengthy;}
     if(slidePosition.y<Screen.height/2){
         strengthy=Screen.height/2-slidePosition.y;
         ;}
     
     else{
         strengthy=slidePosition.y-Screen.height/2;
         }
     strength=Mathf.Sqrt((strengthx*strengthx)+(strengthy*strengthy));
     catapault.transform.localEulerAngles.y=ThrowAngle*-45;
     tension = strength/250;
     
     tileSize = Screen.width/10;
     if(strength>0){
     sling.transform.localScale=Vector3(1,1,tension);    
     
     }
 }
 function OnGUI () {
     screenWidth = Screen.width;
     screenHeight = Screen.height;
    
 
     var xMax : int = Mathf.CeilToInt(tiles.length/3.0f);
     maxSlidePosition.x = -spacer*(xMax+1)-tileSize*(xMax)+screenWidth;
 
     for (var i=0; i<tiles.length; i++){
        var position : float = i+1;
        var xGridPosition : int = Mathf.CeilToInt(position/3.0f);
        var yGridPosition : int = Mathf.CeilToInt(position/3.0f);
        var rect : Rect = new Rect(spacer*xGridPosition+tileSize*(xGridPosition-1)+slidePosition.x, spacer*xGridPosition+tileSize*(xGridPosition-1)+slidePosition.y, tileSize, tileSize);
        var tile : Tile = tiles[i];
        GUI.Box(rect, tile.name);
     }
     GUI.Box(Rect(Screen.width/3, Screen.height/1.5,Screen.width/3, Screen.height/2),"", TargetBack);
     
     
 }
 
 function Missile(){
     
     var clone : Rigidbody;
 
 clone = Instantiate(projectile, spawnpoint.transform.position, catapault.transform.rotation);
 clone.velocity = catapault.transform.TransformDirection (Vector3.forward*strength*.1);
 loadedobject.SetActiveRecursively(false);
 yield WaitForSeconds(1);
 loadedobject.SetActiveRecursively(true);
 }
 
 
 
 
 class Tile{
     var name : String = "indigo button";
     var texture : Texture2D;