<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

<html>
<head>
<title>test</title>

<SCRIPT LANGUAGE="JavaScript">


function calc()
{
if (document.testform.chk.checked) {

document.testform.total.value = document.testform.a1.value +
document.testform.a2.value +
document.testform.a3.value +
document.testform.a4.value ;
document.testform.total.focus();
}
else
{
document.testform.total.value = ""
document.testform.total.blur();
}
}

</SCRIPT>
</head>

<body>
<FORM NAME="testform">
<br>
no 1: <input type="text" name="a1"><br>
no 2: <input type="text" name="a2"><br>
no 3: <input type="text" name="a3"><br>
no 4: <input type="text" name="a4"><br>

<br>
<input type="checkbox" name="chk" onClick="calc();">

합계: <input type="text" name="total">

</FORM>

</body>
</html>