function centerObj(pointer, objHeight) {
  
  var viewportHeight;
  
  if (typeof window.innerWidth != "undefined")
    viewportHeight = window.innerHeight;
  else if (typeof document.documentElement != "undefined" && typeof document.documentElement.clientWidth != "undefined" && document.documentElement.clientWidth != 0)
    viewportHeight = document.documentElement.clientHeight;
  else
    viewportHeight = document.getElementsByTagName('body')[0].clientHeight;
  
  var topMargin = Math.round((viewportHeight - objHeight) / 2);
  
  if (topMargin < 0)
    topMargin = 0;
  
  pointer.style.marginTop = topMargin.toString() + "px";
  
  return;
  
}