title: gnuplot plot discrete(?) time data
body: <p>I should like to gnuplot some data for various devices, where the data is the time those devices are in a certain state. </p>
  
  <p>For example, given devices <em>a</em> to <em>e</em>, plot the time they go into alarm then exit, e.g. device <em>a</em> goes into alarm 11:00, out of alarm at 12:00, etc..</p>
  
  <pre><code>dev_a |   x------x
  dev_b |     x-----x
  dev_c | x-x
  dev_d |           x-------------------
  dev_e |     x-----x       x-----x
        |_______________________________
            |      |     |     |     |
          11:00  12:00 13:00 14:00 15:00
  </code></pre>
  
  <p>The input data would would need to be derived from logs similar to:</p>
  
  <pre><code>    ....
  11:00 dev_a alarm on
      ....
  11:00 dev_c alarm off
  11:10 dev_b alarm on
      ....
  12:00 dev_a alarm off
      ....
  </code></pre>
  
  <p>I am not really sure how to get started&mdash;a column plot of sorts?</p>