function rilchinger_nivellier()
{
 //var thebody = document.getElementById("body").Height;

if (document.body && document.body.offsetHeight)
{
   var thebody =  screen.availheight;
}
else
{


}
  // var thebody = document.all.thebody.innerHeight;
  var thebody = window.innerHeight;
//document.body.offsetHeight; //parent.window..height.height;
   //var z2 = document.getElementById("left-middle").offsetHeight;
  // var z3 = document.getElementById("content-right").offsetHeight;


   var abstand = (thebody - 600)/2;
         alert ( thebody );       /*     */

   document.getElementById("main").style.marginTop   = abstand + 'px';

}