<form id="aform" method="post">
<select id="menucompare" name ="menucompare" size="1">
<option value="nothing" <?php if ($menucompare == "nothing") { echo " selected='selected'"; } ?>>Select one</option>

<option value="mytablevalue1" <?php   if ($menucompare == "mytablevalue1") { echo " selected='selected'"; } ?> >myvalue1</option>
<option value="mytablevalue2" <?php   if ($menucompare == "mytablevalue2") { echo " selected='selected'"; } ?> >myvalue2</option>
<option value="mytablevalue3" <?php   if ($menucompare == "mytablevalue3") { echo " selected='selected'"; } ?> >myvalue3</option>
<option value="mytablevalue4" <?php if ($menucompare == "mytablevalue4") { echo " selected='selected'"; } ?> >myvalue4</option>


</select>
<input type="hidden" name="hidevalue" value="<?php echo $menucompare ;  ?>" />
<noscript><input type="submit" value="Submit"></noscript>
</form>

[removed]

  $(document).ready(function(){
       $("select").change(function() { 
             displayVals(); 
       });
       displayVals();
  });

  function displayVals() {
    var singleValues = $("#menucompare").val();
    $("#hiddenselect").val(singleValues);
    $("p").html("Procent of : &nbsp; &nbsp;" + singleValues);
  }

[removed]