title: Measuring elapsed time in lua (+love2D)
body: <p>I'm trying to measure time of my code execution with the os.time() function and display it with LOVE framework. But, to my surprise, the displayed times are changing...
  My code is: </p>
  
  <pre><code>function foo()
      start_time = os.time()
          &lt;some code&gt;
      end_time = os.time()
      elapsed_time = os.difftime(end_time-start_time)
      love.graphics.print('start time: '   .. start_time .. 's', 12, 12)
      love.graphics.print('end time: '     .. end_time .. 's', 12, 22)
      love.graphics.print('time elapsed: ' .. elapsed_time .. 's', 12, 32)
  end
  </code></pre>
  
  <p>When I leave the window with my graphics open the times are changing (start and end growing and the difference changes between 1 and 2) - so the first question is how does that happen if os.time() returns a number. And also - is that a good way to measure the execution time of my application?</p>