$timezone = round($_POST['timezone'], 1);

// anti-spam code variable checked here. Customize to suit your needs.
 if ($_POST['spamcode'] <> "1492") 
  message('Please enter the correct 4 digit code for the year Columbus discovered America.');

<div class="inform">
<fieldset>
<legend><?php echo $lang_prof_reg['Localisation legend'] ?></legend>

<div class="inform">
<fieldset>
<legend>Spambot prevention</legend>
<div class="infldset">
<p>Please enter the year in which Columbus discovered America in the box below.</p>
<p><b>Hint:</b> </p>
<div class="rbox">
<input type="text" name="spamcode" size="4" maxlength="4" /><br />
</div>
</div>
</fieldset>
</div>