Yevgeniy,
<HTML>
<HEAD>
<script type="text/javascript">
function calc() {
var x = document.getElementById("polotno");
var x = parseFloat(polotno.value);
result.innerHTML = x;
}
</script>
</HEAD>
<BODY>
<select style='width: 150px;' onchange='calc()' id='polotno'>
<option value='1'>1</option>
<option value='2'>2</option>
<option value='3'>3</option>
</select>
<BR>
<span id='result'></span>
<script type="text/javascript">
calc()
</script>
</BODY>
</HTML>