ช่วยดูโค๊ดทีครับ Loop ตัว Auto sum แล้วไม่ออก แต่ถ้าไม่ Loop ออกครับ

$cnt=count($_SESSION['smat_id']);

echo "<form method='post' action='recalculate.php' name='form1'>";
echo "<table class='table table-striped table-bordered table-hover' id='dataTables-example'>";
 echo "<tr><th><center>ยกเลิก</center></th><th><center>รหัสวัสดุ</center></th><th><center>ชื่อวัสดุ</center></th><th><center>จำนวนคงเหลือ</center></th><th><center>หน่วยนับ</center></th><th><center>ประเภท</center></th><th><center>ราคาต่อหน่วย</center></th><th><center>จำนวนที่จะสั่งซื้อ</center></th><th><center>ราคารวม</center></th></tr>";

$u=$_SESSION['smat_unit'];
$t=$_SESSION['smat_type'];    
$id=$_SESSION['smat_id'];

 for($i=0;$i<$cnt;$i++){
       $sql3=mysql_query("SELECT price_unit FROM stock WHERE mat_id='$id[$i]'");
       list($pu)=mysql_fetch_row($sql3);

        $sql=mysql_query("SELECT mat_unit_name FROM unit WHERE mat_unit_id='$u[$i]'");
        list($unit)=mysql_fetch_row($sql);

        $sql2=mysql_query("SELECT mat_type_name FROM type WHERE mat_type_id='$t[$i]'");
        list($type)=mysql_fetch_row($sql2);

echo "<tr><td align='center'><input type='checkbox' name='cancel_id[]' value='",$id[$i],"'></td>";
echo "<td align='center'>",$id[$i],"</td>";
echo "<td align='center'>",$_SESSION['smat_name'][$i],"</td>";
echo "<td align='center'>",$_SESSION['smat_stock'][$i],"</td>";
echo "<td align='center'>",$unit,"</td>";
echo "<td align='center'>",$type,"</td>";
 echo " <td><input name='price_unit[]' id='txtVol1_[$i]' value='$pu' OnChange='JavaScript:fncCal();' type='text'> </td>
<td><input name='amount[]' id='txtVol2_[$i]' OnChange='JavaScript:fncCal();' type='text'></td>
<td><input name='sum[]' id='txtVol3_[$i]' type='text'><br></td></tr>";
                                
echo "<input type='hidden' name='hdnLine' value='$cnt'>"; 
                      }   
echo "</table>";

<script language="javascript">
function fncCal()
{
    var tot = 0;
    var sum = 0;
    for(i=0;i<=document.form1.hdnLine.value;i++)
    {
        tot = parseInt(eval("document.form1.txtVol1_"+i+".value")) * parseInt(eval("document.form1.txtVol2_"+i+".value"))
        eval("document.form1.txtVol3_"+i+".value="+tot);
        sum = tot + sum;
        document.form1.txtSum.value=sum;
    }
}
</script>