Не получается вывести значение option value в input
<!DOCTYPE html>
<html>
<head>
<title>Селекты</title>
<meta charset="utf-8">
</head>
<form > <select id="reg" size="1">
<option value="0.1">0.1</option>
<option value="0.5">0.5</option>
<option value="1">1</option></select>
</form>
<script type="text/javascript">
function calculat (obj) {
var myselect = document.getElementById("reg");
var select_value = myselect.value;
obj.res3.value= select_value;
}
</script><input type="text" style="width:55px" id="res3">
<input type="button" name="WB" value="Ok" onclick="calculat(form)">
</html>