// hoogte en breedte van bepaalde delen van het scherm opvragen
    function schermpixelbeheer()
    {
	  this.bottom = function(){
		if (document.body.scrollHeight) return document.body.scrollHeight};

	  this.height = function() {
		if (document.body.offsetHeight) return document.body.offsetHeight;}

	  this.visHeight = function() {
		if (window.innerHeight) return window.innerHeight;
		else if (document.documentElement && document.documentElement.clientHeight) return document.documentElement.clientHeight;
		else if (document.body.clientHeight) return document.body.clientHeight;}

	  this.width = function() {
		if (document.body.offsetWidth) return document.body.offsetWidth;}

	  this.scrollTop = function() {
		if (self.pageYOffset) return self.pageYOffset;
		else if (document.documentElement && document.documentElement.scrollTop) return document.documentElement.scrollTop;
		else if (document.body) return document.body.scrollTop;
		else return 0;};
    }
	
	var newtop = 0;
	var oldtop = 400;
	var arrowTimerID;
	var windowTimer;

	function movetotop() {
	  obj = document.getElementById("arrowup");
	  if (oldtop<newtop) {
	    d = newtop-oldtop;
		s = (d - (d % 5)) / 5;

	    oldtop = oldtop+s;
		obj.style.top = oldtop+"px";
	  }
	  if (oldtop>newtop) {
	    d = oldtop-newtop;
		s = (d - (d % 5)) / 5;

	    oldtop = oldtop-s;
		obj.style.top = oldtop+"px";
	  }

	  if (oldtop==newtop) {
	    clearTimeout(arrowTimerID);
	  }
	}

	function Navigatiebalk()
	{

	  if (document.getElementById("arrowup")) {
	  obj = document.getElementById("arrowup");
	  obj.style.left = 1;
	  /* ((document.body.offsetWidth-742)/2)+20; */
      newtop  = (rdScherm.scrollTop()+(rdScherm.visHeight()-50));
	  arrowTimerID = setTimeout('movetotop()',1); 
	  /* obj.style.top = newtop+"px"; */
	 }
	}

	function windhoosss()
	{
      Navigatiebalk();
	}
	

    var rdScherm=new schermpixelbeheer();
    windowTimer=setInterval("Navigatiebalk()",15);
    window.onresize=windhoosss;
    window.onload = Navigatiebalk;