Movement speed difference between the different devices

I just making a ball game with Unity, but in every device (android) the speed is different I read some docs about Timedelta but I understand nothing. could you please describe me how can I stabilize the speed in every device? here is my script.

#pragma strict
var Right = 30;
var Left = 30;
var LeftButton : GUITexture;
var RightButton : GUITexture;

function Awake () {

LeftButton = GameObject.Find("LeftButton").guiTexture;
RightButton = GameObject.Find("RightButton").guiTexture;


}



function Update () {

for (var touch : Touch in Input.touches)
{

if (touch.phase == TouchPhase.Stationary && LeftButton.HitTest (touch.position))
//if (Input.GetKey("left"))
{
rigidbody.AddForce(Vector3.left * Left) ;
}
//if (Input.GetKey("right"))

if (touch.phase == TouchPhase.Stationary && RightButton.HitTest (touch.position))
{
rigidbody.AddForce(Vector3.right * Right) ;
}

}


}

Multiply your forces by Time.deltaTime, for example:

rigidbody.AddForce(Vector3.right * Right * Time.deltaTime)