function zentrum() {
				    var y 
				    if (self.innerHeight) // all except Explorer
					{
						y = self.innerHeight / 2;
						
					}
					else if (document.documentElement && document.documentElement.clientHeight)
						// Explorer 6 Strict Mode
					{
						y = document.documentElement.clientHeight / 2;
					}
					else if (document.body) // other Explorers
					{
						y = document.body.clientHeight / 2;
					}			
					var z = document.getElementById('f_inhalt').style.height;
					var test_array=z.split("px");
					z = (test_array[0] / 2) + 20;
					document.getElementById('vertikal').style.top = Math.max(z,y) + 'px';	
	}