ขอคำแนะนำ เรื่องการคำนวนค่าจาก Checkbox ค่ะ ช่วยได้ค่ะ

<script language="javascript">
<!--
	function checksum(obj){
		lblObj = document.getElementById('lblmsg');
		lblValue =  (lblObj.innerText == "")?0:lblObj.innerText;
		
		//alert(obj.checked)
		if (obj.checked == true){
			lblObj.innerText = parseInt(lblValue) + parseInt(obj.value);
		}else{
			lblObj.innerText = parseInt(lblValue) - parseInt(obj.value);
		}
	}
//-->
</script>
<input type="checkbox" id="chk1" value="10" onclick="checksum(this)"> ค่าเป็น 10 <br>
<input type="checkbox" id="chk2" value="5" onclick="checksum(this)">ค่าเป็น 5 <br>
<label id="lblmsg"></label>

<script language="javascript">
<!--
	var labelValue = "";

	function checksum(obj){
		lblObj = document.getElementById('lblmsg');
		lblValue =  (lblObj.innerText == "")?0:lblObj.innerText;
		
		//alert(obj.checked)
		if (obj.checked == true){
			lblObj.innerText = parseInt(lblValue) + parseInt(obj.value);
		}else{
			lblObj.innerText = parseInt(lblValue) - parseInt(obj.value);
		}
		
		labelValue = lblObj.innerText;
	}
	
	function sendToPhp(){
		lblObj = document.getElementById('lblmsg');
		var sPath = window.location.pathname;
		var sPage = sPath.substring(sPath.lastIndexOf('/') + 1);
		//alert(sPage);

		strLocation =  sPath + '?label=' 
		strLocation += (labelValue == "")?lblObj.innerText:labelValue;
		self.location.replace(strLocation);
	}
//-->
</script>
<input type="checkbox" id="chk1" value="10" onclick="checksum(this)"> ค่าเป็น 10 <br>
<input type="checkbox" id="chk2" value="5" onclick="checksum(this)">ค่าเป็น 5 <br>
<label id="lblmsg">2000</label><br>
<input type="button" value="ส่งค่าให้ php" onclick="sendToPhp()">
<?
	echo "ค่าที่ได้จาก php =====>" . $_GET["label"];
?>

	function sendToPhp(){
		lblObj = document.getElementById('lblmsg');
		var sPath = window.location.pathname;
		var sPage = sPath.substring(sPath.lastIndexOf('/') + 1);
		//alert(sPage);

		strLocation =  sPath + '?label=' 
		strLocation += (labelValue == "")?lblObj.innerText:labelValue;
		self.location.replace(strLocation);
	}

	function sendToPhp(){
		lblObj = document.getElementById('lblmsg');
		chk1 = document.getElementById('chk1');
		chk2 = document.getElementById('chk2');
		
		var sPath = window.location.pathname;
		var sPage = sPath.substring(sPath.lastIndexOf('/') + 1);
		//alert(sPage);

		strLocation =  sPath + '?label=' 
		strLocation += (labelValue == "")?lblObj.innerText:labelValue;
		strLocation += "&chk1=" + chk1.value + "&chk2=" + chk2.value;
		self.location.replace(strLocation);
	}

echo "ค่าที่ได้จาก php =====>" . $_GET["label"];

<?
	echo "ค่าที่ได้จาก php =====>" . $_GET["label"] . "<br>";
	echo "ค่าที่ได้จาก ดินสอ =====>" . $_GET["chk1"] . "<br>";
	echo "ค่าที่ได้จาก ปากกา =====>" . $_GET["chk2"] . "<br>";
	
?>