title: Calculate duration using Date.Time.Now in C#
body: <p>I need to calculate duration for my system running. My system in c#.
  I've set:</p>
  
  <pre><code>DateTime startRunningProg = Date.Time.Now("o");
  </code></pre>
  
  <p>after a few process.</p>
  
  <p>I set :</p>
  
  <pre><code>DateTime endRunningProg = Date.Time.Now("o");
  </code></pre>
  
  <p>How to calculate duration for my system running in millisec or sec.</p>