Varför funkar inte detta i NS6?

Varför fungerar inte detta i Netscape 6?

<script language="JavaScript">
<!--
function Calculate()
{
	var a1 = parseFloat(document.testform1.int1.value);
	document.testform1.int2.value = a1*1.5 + 5;

	var a2 = parseFloat(document.testform1.int2.value);
	var a3 = parseFloat(document.testform1.int3.value);
	document.testform1.int4.value = a2 + a3 + 10;

	var a4 = parseFloat(document.testform1.int4.value);

	document.testform1.int5.value = a4 * 2;
	var a5 = parseFloat(document.testform1.int5.value);

	document.testform1.svar.value = a5 + 1
}
//-->
</script>

Funktionen anropas med en knapp i ett formulär:

<form name="testform1" action="test.asp" method="post" >
  <input type="text" name="int1">
  <br>
  <input type="text" name="int2">
  <br>
  <input type="text" name="int3">
  <br>
  <input type="text" name="int4">
  <br>
  <input type="text" name="int5">
  <br>
  <br>
  <input type="text" name="svar">
  <br>
  <br>
  <input type="button" name="Button" value="Calculate" onClick="javascript:Calculate()">
</form>

Det fungerar utmärkt i IE5.