function show2levens() {
    if(window.ie) {
        $('tweelevens').setStyle('display','block');
    } 
    else {
        $('tweelevens').setStyle('display','table-row-group');
    }
}

function hide2levens() {
    $('tweelevens').setStyle('display','none');
}

function berekenen() {    
    
		var url       = '../includes/ajax.php';
		var request   = new Ajax(
			url, {
			method: 'post',
			postBody: $('berekenaar'),
			onComplete: function(){
			    $('resultaat').innerHTML = this.response.text;
			    $('resultaat').setStyle('display','block')

			},
			evalScripts: true
		});

		request.setHeader('Content-Type','application/x-www-form-urlencoded'); 
		request.request();
}