ขอแนวทางหน่อยครับ ติดปัญหาการรวมจำนวน รวมได้แต่พอแก้ไข แล้วกลับไม่ได้

function addbox(){ 
	var b=document.getElementById('inputboxes' ); 
	var el1=document.createElement("br" ); 
	var el2=document.createElement("input"); 
	var el3=document.createTextNode(" "); 
	var el4=document.createElement("input"); 
	var el5=document.createTextNode(" "); 
	var el6=document.createElement("input"); 
	var el7=document.createTextNode(" "); 
	var el8=document.createElement("input"); 
	var el9=document.createTextNode(" "); 
	var el10=document.createElement("input"); 
	var el11=document.createTextNode(" "); 
	var el12=document.createElement("input"); 
	var el13=document.createTextNode(" "); 
	var el14=document.createElement("input"); 
	var el15=document.createTextNode(" "); 
	var el16=document.createElement("input"); 
	var el17=document.createTextNode(" "); 
	var el18=document.createElement("input");
var count=document.getElementById('row-count').value*1; 
		count++; 
	document.getElementById('row-count').value=count; 

el2.name='data['+count+'][PDCode]'; 
el2.id='data['+count+'][PDCode]'; 
el2.type='text'; 
el2.value=''; 
el2.size='7';
el2.maxlength='20';
el2.tabindex='1';
el2.onkeyup=function(){ doCallAjax('data['+count+'][PDCode]','data['+count+'][PDName]','data['+count+'][Price]','data['+count+'][Price2]');}

el4.name='data['+count+'][PDName]'; 
el4.id='data['+count+'][PDName]'; 
el4.type='text'; 
el4.value='';   
el4.size='18';
el4.readonly='readonly';

el6.name='data['+count+'][Quantity]'; 
el6.id='data['+count+'][Quantity]'; 
el6.type='text'; 
el6.value='';
el6.size='2';
el6.maxlength='5';
el6.tabindex='2';
el6.onkeyup=function(){ chksum('G',count);}


el8.name='data['+count+'][Price]'; 
el8.id='data['+count+'][Price]'; 
el8.type='text'; 
el8.value='';        
el8.size='5';
el8.readonly='readonly';

el10.name='data['+count+'][Price2]'; 
el10.id='data['+count+'][Price2]'; 
el10.type='text'; 
el10.value='';        
el10.size='5';
el10.readonly='readonly';

el12.name='data['+count+'][PricePerPiece]'; 
el12.id='data['+count+'][PricePerPiece]'; 
el12.type='text'; 
el12.value='';      
el12.size='7';
el12.maxlength='10';
el12.tabindex='3';
el12.onkeyup=function(){ chksum('D',count);chksum('E',count);chksum('F',count);}

el14.name='data['+count+'][Dis_baht]';  
el14.id='data['+count+'][Dis_baht]';  
el14.type='text'; 
el14.value='';  
el14.size='7';
el14.readonly='readonly';

el16.name='data['+count+'][Dis_Percent]'; 
el16.id='data['+count+'][Dis_Percent]'; 
el16.type='text'; 
el16.value='';  
el16.size='3';
el16.readonly='readonly';

el18.name='data['+count+'][Amount]'; 
el18.id='data['+count+'][Amount]'; 
el18.type='text'; 
el18.value='';    
el18.size='8';
el18.readonly='readonly';
el18.onblur=function() { addbox();return false;}

b.appendChild(el1); 
b.appendChild(el2); 
b.appendChild(el3); 
b.appendChild(el4); 
b.appendChild(el5); 
b.appendChild(el6); 
b.appendChild(el7); 
b.appendChild(el8); 
b.appendChild(el9); 
b.appendChild(el10); 
b.appendChild(el11); 
b.appendChild(el12); 
b.appendChild(el13); 
b.appendChild(el14); 
b.appendChild(el15); 
b.appendChild(el16); 
b.appendChild(el17); 
b.appendChild(el18); 
document.getElementById('data['+count+'][PDCode]').focus();
}

<input type="hidden" id="hidquantity" value="" />
<table width="634" cellspacing="1" border="1" bordercolor="#3DB179">
			  <tr>
				<td width="207" align="center" bgcolor="#A4E4DD">รวม</td>
				<td width="33" align="center" bgcolor="#A4E4DD"><input name="sumquantity" id="sumquantity" type="text" value="" size="2" readonly="true" style="background:#A4E4DD;"/>
				<td width="313" align="center" bgcolor="#A4E4DD">&nbsp;</td>
				<td width="74" align="center" bgcolor="#A4E4DD"><input name="sumamount" id="sumamount" type="text" value="" size="8" readonly="true" style="background:#A4E4DD;"/></td>
				<!-- <td width="333" align="center" bgcolor="#A4E4DD" rowspan="3">&nbsp;</td> -->
			  </tr>
			  <tr>
				<td width="207" align="center" bgcolor="#FFFFCC">ผลรวมจากใบขอ</td>
				<td width="33" align="center" bgcolor="#FFFFCC"><input name="plazaquantity" type="text" value="" size="2"/>
				<td width="313" align="center" bgcolor="#FFFFCC">&nbsp;</td>
				<td width="74" align="center" bgcolor="#FFFFCC"><input name="plazaamount" type="text" value="" size="8"/></td>
			  </tr>
			  <tr>
				<td width="207" align="center" bgcolor="#A4E4DD">ผลต่าง</td>
				<td width="33" align="center" bgcolor="#A4E4DD"><input name="difquantity" type="text" value="" size="2" readonly="true" style="background:#A4E4DD;"/>
				<td width="313" align="center" bgcolor="#A4E4DD">&nbsp;</td>
				<td width="74" align="center" bgcolor="#A4E4DD"><input name="difamount" type="text" value="" size="8" readonly="true" style="background:#A4E4DD;"/></td>
			  </tr>
			</table>

function chksum(chk,count){
	var a = document.getElementById('data['+count+'][Quantity]').value
	var b = document.getElementById('data['+count+'][Price]').value
	var c = document.getElementById('data['+count+'][Price2]').value
	var d = document.getElementById('data['+count+'][PricePerPiece]').value
	var e = document.getElementById('data['+count+'][Dis_baht]').value
	var f = document.getElementById('data['+count+'][Dis_Percent]').value
	var g = document.getElementById('data['+count+'][Amount]').value
	var h = document.getElementById('hidquantity').value
	var i = document.getElementById('sumquantity').value

	if(chk=="D"){
		if(c=="0.00"){
		document.getElementById('data['+count+'][Dis_baht]').value=-((d*1)-(b*1));
		document.getElementById('data['+count+'][Dis_baht]').style.backgroundColor = "#A4E4DD";
		document.getElementById('data['+count+'][Dis_baht]').readOnly = true;
		}else{
		document.getElementById('data['+count+'][Dis_baht]').value=(d*1)-(c*1);
		document.getElementById('data['+count+'][Dis_baht]').style.backgroundColor = "#A4E4DD";
		document.getElementById('data['+count+'][Dis_baht]').readOnly = true;
		}
	}

	if(chk=="E"){
		var numf = document.getElementById('data['+count+'][Dis_Percent]').value=100-((d/b)*100);
		document.getElementById('data['+count+'][Dis_Percent]').value = parseFloat(numf).toFixed(0)+'%';
		document.getElementById('data['+count+'][Dis_Percent]').style.backgroundColor = "#A4E4DD";
		document.getElementById('data['+count+'][Dis_Percent]').readOnly = true;
	}
	if(chk=="F"){
		document.getElementById('data['+count+'][Amount]').value=a*1*d;
		document.getElementById('data['+count+'][Amount]').style.backgroundColor = "#A4E4DD";
		document.getElementById('data['+count+'][Amount]').readOnly = true;
	}
	if(chk=="G"){
		document.getElementById('hidquantity').value=a;
		document.getElementById('sumquantity').value=(i*1)+(a*1);
	}
}