You are not allowed to call get_rigidbody when declaring a variable.

Questions & Answers
1

When using the speedometer script below im getting the error:

ArgumentException: You are not allowed to call get_rigidbody when declaring a variable. Move it to the line after without a variable declaration. Don't use this function in the constructor or field initializers, instead move initialization code to the Awake or Start function. NumericalSpeedometer..ctor () (at Assets/Scripts/JavaScripts/GUIScripts/NumericalSpeedometer.js:2)

How can i call the rigidbody from a the awake/start function?

var car = rigidbody;
private var mph = 0;
var gSkin : GUISkin;

function Awake (){

}
function Update(){
  var speed = car.velocity.magnitude * 2.237;
  mph = speed;
}

function OnGUI(){

if (gSkin)
GUI.skin = gSkin;
else
Debug.Log("StartMenuGUI: GUI Skin object missing!");

GUI.Box(new Rect(30, Screen.height - 100, 40, 70), "" + mph, "Speedometer");
}
2 
var car : Rigidbody;

//...

function Awake () {
   car = rigidbody;
}

//...