How To Get Total Value Of Textbox In Loop

<script language="javascript">
function getTotal(i){
var tot = 0;
var total=0;
var totalaccurate=0;
var tbys = document.getElementById('blw'+i).value;
var total=document.frmtot.totblw.value;
if(tbys ==""){
tbys = 0;
}if(total ==""){
total = 0;
}var tot1 = parseInt(tbys) + parseInt(total);
document.frmtot.totblw.value = tot1;
}
</script>

The above script is ok if entering the value first time. But when the user changes the value in any text box, it seems to add incorrectly. It adds what was already in the textboxes, then adds it again. How to display the correct value every time the user changes a value in one of the text boxes.