Average value of list
<p>I want to make code that will on the first click start <code>rotorSpeed</code> stopwatch then on the second click add <code>rotorSpeed.ElapsedMilliseconds</code> to <code>list</code>. On the second click resets stopwatch and starts timing again, then on the third click again adds <code>rotorSpeed.ElapsedMilliseconds</code> to <code>list</code>.
There are no errors in the code, but when I debug it, I get an error on <code>double average = list.Average();</code></p>

<p><code>Stopwatch rotorSpeed = new Stopwatch();
 List&lt;double&gt; list = new List&lt;double&gt;();</code></p>

<pre><code>private void button1_Click(object sender, EventArgs e)
{
    i++;
    //Getting rotor speed
    if (i != 2)
    {               
        if (rotorSpeed.IsRunning)
        {
            rotorSpeed.Stop();
            list.Add(rotorSpeed.ElapsedMilliseconds);
            rotorSpeed.Start();                   
        }
        else
        {
            rotorSpeed.Reset();
            rotorSpeed.Start();
        }
    }

    double average = list.Average();
    textBox2.Text = average.ToString();
}
</code></pre>

<p>This is the error I get:</p>

<blockquote>
  <p>An unhandled exception of type 'System.InvalidOperationException' occurred in >System.Core.dll</p>
  
  <p>Additional information: Sequence contains no elements</p>
</blockquote>