How to make a helicopter speed gauge?

Im trying to build a speed gauge HUD for my helicopter that uses the rotor velocity to indicate the rotor speed rather than using rigidbody to calculate. I want to link the rotor's velocity(which I have the script in my helicopter) to my speed gauge HUD. What code should I use to link the rotor velocity to the speed gauge HUD?

Here is the current code that I have,

 var gaugeTex: Texture2D;

var pointTex: Texture2D;

var gaugePos: Vector2;

var topSpeed: float;

var stopAngle: float;

var topSpeedAngle: float;

var speed: float;

var player_gameobject : GameObject;

private var helicopter_throttle : float;

function OnGUI() {

 GUI.DrawTexture(Rect(gaugePos.x, gaugePos.y, gaugeTex.width, gaugeTex.height), gaugeTex);

 var centre = Vector2(gaugePos.x + gaugeTex.width / 2, gaugePos.y + gaugeTex.height / 2);

 var savedMatrix = GUI.matrix;

 var speedFraction = speed / topSpeed;

 var pointAngle = Mathf.Lerp(stopAngle, topSpeedAngle, speedFraction);

 GUIUtility.RotateAroundPivot(pointAngle, centre);

 GUI.DrawTexture(Rect(centre.x, centre.y - pointTex.height / 2, pointTex.width, pointTex.height), pointTex);

 GUI.matrix = savedMatrix;

     helicopter_throttle = player_gameobject.GetComponent( "Heli Flight Script" ).rotor_Velocity;    

}

function Update() {

speed = helicopter_throttle;

}

Any Help is appreciated