...
<select name="metric" size="1">
<option value="b" <? if($mtr=='b') echo "selected";?>>Bytes</option>
<option value="k" <? if($mtr=='k') echo "selected";?>>KBytes</option>
<option value="m" <? if($mtr=='m') echo "selected";?>>MBytes</option>
</select>
...

<tr><td>Pole</td></tr>