Create Stop Watch Application in ASP.Net example

I done my c# code to stop watch

    protected void tm1_Tick(object sender, EventArgs e)
    {
        long sec = sw.Elapsed.Seconds;
        long min = sw.Elapsed.Minutes;
        long hour = sw.Elapsed.Hours;
        Label1.Text = hour.ToString("00") + ":" + min.ToString("00") + ":" + sec.ToString("00");
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        sw = new Stopwatch();
        sw.Start();
    }

    protected void Button2_Click(object sender, EventArgs e)
    {
        sw.Stop();
    }
}

This is my c# code

When i stop the stop watch i want to display the stopped time in msg box how i get it?????