title: Compute the duration of appointment in an org-mode table
body: <p>I have a list of appointments in the style of:</p>
  
  <pre><code>| Appointment                  | Dur.  |
  |------------------------------+-------|
  | &lt;2014-02-20 Thu 09:30-18:30&gt; |  ???  |
  | &lt;2014-02-22 Sat 09:00-10:00&gt; |  ???  |
  |                              |       |
  </code></pre>
  
  <p>How can I make orgmode calculate the durations of my appointments?</p>