How to Calculate sum of number onchange event.

<SCRIPT LANGUAGE="JavaScript">
<!--
function sumIt(theName) {
theName = theName.substr(0,theName.length-1)
var f = document.forms["myForm"]
var s = 0
for (var i=1;i<=4;i++) {
var v = f.elements[theName+i].value
v = parseFloat(v)
if (isNaN(v)) continue
v = Math.abs(v)
s+=v
}
f.elements[theName + "total"].value = s

}
//-->
</SCRIPT>
<form name="myForm">
Val
<p>
one: <input type=text name="Val1" onchange="sumIt(this.name)">
</p>
<p>
two: <input type=text name="Val2" onchange="sumIt(this.name)">
</p>
<p>
three: <input type=text name="Val3" onchange="sumIt(this.name)">
</p>
<p>
four; <input type=text name="Val4" onchange="sumIt(this.name)">
</p>
<p>
Suma:<input type="text" READONLY class="disabled" name="Valtotal" size="20" value="0.00">
</p>
<br>