function myPopupRelocate() {
	  var scrolledX, scrolledY;
	  if( self.pageYOffset ) {
		scrolledX = self.pageXOffset;
		scrolledY = self.pageYOffset;
	  } else if( document.documentElement && document.documentElement.scrollTop ) {
		scrolledX = document.documentElement.scrollLeft;
		scrolledY = document.documentElement.scrollTop;
	  } else if( document.body ) {
		scrolledX = document.body.scrollLeft;
		scrolledY = document.body.scrollTop;
	  }

	  var centerX, centerY;
	  if( self.innerHeight ) {
		centerX = self.innerWidth;
		centerY = self.innerHeight;
	  } else if( document.documentElement && document.documentElement.clientHeight ) {
		centerX = document.documentElement.clientWidth;
		centerY = document.documentElement.clientHeight;
	  } else if( document.body ) {
		centerX = document.body.clientWidth;
		centerY = document.body.clientHeight;
	  }

	  var leftOffset = scrolledX + (centerX - 390) / 2;
	  var topOffset = scrolledY + (centerY - 350) / 2;

	  document.getElementById("mypopup").style.top = topOffset + "px";
	  document.getElementById("mypopup").style.left = leftOffset + "px";
	}

	function fireMyPopup() {
	  myPopupRelocate();
	  document.getElementById("mypopup").style.display = "block";
	  document.body.onscroll = myPopupRelocate;
	  window.onscroll = myPopupRelocate;
	}

	function bmi(lengte,gewicht) {

		if(lengte == '' || gewicht == '') {

			alert('Je moet wel de gegevens correct invullen...');

		}
		else {

			var kwadraat = (lengte / 100) * (lengte / 100);
			var bmi = Math.round((gewicht / kwadraat) * 10) / 10;

			ajaxFunction(bmi);

		}

	}

	function ajaxFunction(bmiscore){
		var ajaxRequest;  // The variable that makes Ajax possible!
		
		try{
			// Opera 8.0+, Firefox, Safari
			ajaxRequest = new XMLHttpRequest();
		} catch (e){
			// Internet Explorer Browsers
			try{
				ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
			} catch (e) {
				try{
					ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
				} catch (e){
					// Something went wrong
					alert("Your browser broke!");
					return false;
				}
			}
		}
		// Create a function that will receive data sent from the server
		ajaxRequest.onreadystatechange = function(){
			if(ajaxRequest.readyState == 4){
				var lengte = document.getElementById('lengte').value;
				var gewicht = document.getElementById('gewicht').value;

				document.getElementById('bmiscore').innerHTML = '<h3>Jouw BMI: ' + bmiscore + '</h3><br />';
				document.getElementById('bmitekst').innerHTML = ajaxRequest.responseText;
				
				document.getElementById('bmi_graph').innerHTML = '<img src="graph.php?lengte=' + lengte + '&gewicht=' + gewicht + '" />';
				
			}
		}
		var email = document.getElementById('email').value;
		ajaxRequest.open("GET", "http://www.bmi-berekenen.nl/xml.php?bmi=" + bmiscore + "&email=" + email, true);
		ajaxRequest.send(null); 
	}