function roundNumber(rnum, rlength) { // Arguments: number to round, number of decimal places
  var newnumber = Math.round(rnum*Math.pow(10,rlength))/Math.pow(10,rlength);
  return newnumber; // Output the result to the form field (change for your purposes)
}

function calculateRate() {

	var carat = document.getElementById('carat').value;
	var weight = document.getElementById('goldweight').value;
	var rate;
	var payment;
	
	switch(carat) {
		case "9" : rate = 4.47; break;
		case "14" : rate = 6.97; break;
		case "18" : rate = 8.94; break;
		case "20" : rate = 9.93; break;		
		case "22" : rate = 10.92; break;
		default: return false;
	}
	
	payment = rate * weight;
	
	//document.getElementById('result').innerHTML = "£" + roundNumber(payment, 2);
	document.getElementById('result').innerHTML = "£" + payment.toFixed(2);
	return false;
}