Pinch not working

Hi, i have code for scale my objects using pinch. But it's not working, can anyone tell me please?

 using UnityEngine;
 using System.Collections;
 
 public class Zoom_Button : MonoBehaviour 
 {
     private Transform Table_Transform = null;
     
     public float scaleFactor = 0.5f;        // The rate of change of the scale
     
     public float minScale = 0.6f;
     public float maxScale = 2.0f;
     
     void Update()
     {
         // If there are two touches on the device...
         if (Input.touchCount == 2) {
             // Store both touches.
             Touch touchZero = Input.GetTouch (0);
             Touch touchOne = Input.GetTouch (1);
             
             // Find the position in the previous frame of each touch.
             Vector2 touchZeroPrevPos = touchZero.position - touchZero.deltaPosition;
             Vector2 touchOnePrevPos = touchOne.position - touchOne.deltaPosition;
             
             // Find the magnitude of the vector (the distance) between the touches in each frame.
             float prevTouchDeltaMag = (touchZeroPrevPos - touchOnePrevPos).magnitude;
             float touchDeltaMag = (touchZero.position - touchOne.position).magnitude;
             
             // Find the difference in the distances between each frame.
             float deltaMagnitudeDiff = prevTouchDeltaMag - touchDeltaMag;
             
             Table_Transform.localScale += new Vector3(deltaMagnitudeDiff * scaleFactor, deltaMagnitudeDiff * scaleFactor, deltaMagnitudeDiff * scaleFactor); 
             
             float Table_X, Table_Y, Table_Z;
             
             Table_X = Mathf.Clamp(Table_Transform.localScale.x, minScale, maxScale);
             Table_Y = Mathf.Clamp(Table_Transform.localScale.y, minScale, maxScale);
             Table_Z = Mathf.Clamp(Table_Transform.localScale.z, minScale, maxScale);
             
             Table_Transform.localScale = new Vector3(Table_X, Table_Y, Table_Z);
         } 
     }
 }

This is the code. Here it didn't show any errors.

-Prasanna