title: Determine if zoom if vertical or horizontal
body: <p>How would you determine in a zoomCallback function if the zoom was X-Zoom or Y-Zoom ?</p>
  
  <p>The idea is to trigger a server query on X-Zoom and not on Y-Zoom.</p>
  
  <p>Both the timestamp and Y range values slightly change in the 2 kind of zoom. </p>
  
  <p>Any suggestion ?</p>