c# - How to rotate within a fixed interval in Unity?

I have very recently started to learn Unity.

I'm trying to write code that will make a character swing a flag. I want to use this object and rotate the arm up and down. So I need to make it rotate up and down with within 30 degrees.

This is my attempt but it simply keeps on turning. How would I make the hand rotate in motion within the interval [-30, 30] degrees.

private GameObject myobject;
public float timeElapsed =0;
public float delay = 3.0f;
float OO = 0.0f;

void Start () {
    myobject = GameObject.Find ("rightarm").gameObject;
}


void Update () {        
    timeElapsed += Time.deltaTime;
    Debug.Log (timeElapsed);

    if (timeElapsed >= delay) {
        OO = 30.0f;
        timeElapsed = 0;
        if (myobject.renderer.enabled == false) {
            myobject.renderer.enabled = true;
        }


        myobject.transform.Rotate (OO, 0.0f, 0.0f);
    }
    else
    {
        myobject.transform.Rotate (-OO,0.0f, 0.0f );
    }
}