function wheel(event)
{
	var delta = 0;

	// ie event handler
	if (!event) {
		event = window.event;
	}

	// ie Opera
	if (event.wheelDelta) {
		delta = event.wheelDelta/120;

		// kpera korrektur
		if (window.opera){
			delta = -delta;
		}

	// mozilla
	} else if (event.detail) {
		delta = -event.detail/3;
	}

	// wenn gescrollt wird tue dies
	if (delta){
		setZoom(delta);
	}

	// mozilla scrolling verhindern
	if (event.preventDefault){
		event.preventDefault();
	}

	// ie opera scrolling verhindern
	event.returnValue = false;
}

function dowheel()
{
  // scroll listener hinzufügen
  if (window.addEventListener){
    // mozilla
    window.addEventListener('DOMMouseScroll', wheel, false);
  }

  // ie opera
  window.onmousewheel = document.onmousewheel = wheel;
}

function stopwheel()
{
  // scroll listener hinzufügen
  if (window.removeEventListener){
    // mozilla
    window.removeEventListener('DOMMouseScroll', wheel, false);
  }

  // ie opera
  window.onmousewheel = document.onmousewheel = '';
}