Hmm remarkable things?

Hello again.
Thanks for last answere. It works very well but now I have another
remarkable things. Perhaps logic but not for me yet..

I have this source code: (In norwegian but I translate my thoughts through
it in english.)

The problem with this source code is that it work very well if I select one
single item and post it. But when select 2 or more items the same amount
are filled in all field named stk_pa_lager in the database.

// count and increase the amount of tubes.
if(isset($_POST['oppdater_antall_stk_rorladning'])){

// Get store
    $valgt_lager = $_POST['valgt_lager'];

// Get serial number   (Array <input type="number" name="varenr[] size="3">)
  $varenr = $_POST['varenr'];

// number of items in store
    $stk_pa_lager = $_POST['stk_pa_lager'];

// Create an array (<input type="number"
name="oppdater_antall_stk_rorladning[] size="3">)
    $oppdater_antall_stk_rorladning =
$_POST['oppdater_antall_stk_rorladning'];

// Extract the array and save it induvidual as items in $rorladning
    foreach($oppdater_antall_stk_rorladning as $rorladning){

// Multiply and add new items to that one already is in store
        $oppdatert_antall_stk_rorladning = $stk_pa_lager + $rorladning;

// Extract serialnumber and save them one by one in $vnr
    foreach($varenr as $vnr){

// Connect to MySQL database
    include('../../tilkobling.php');

// Update table rorladning
    $sql = "UPDATE rorladning SET stk_pa_lager =
'$oppdatert_antall_stk_rorladning' WHERE valgt_lager = '$valgt_lager' AND
varenr = '$vnr'";
    mysql_query($sql, $tilkobling) or die(mysql_error());

        }

// Output the result to screen
        echo "<p>R&oslash;rladning med varenr: <b>$vnr</b> er oppdatert fra
<b>$stk_pa_lager</b> til <b>$oppdatert_antall_stk_rorladning</b> p&aring;
lager: <b>$valgt_lager</b>.</p>";
        //echo "$oppdatert_antall_stk_rorladning<br>";
    unset($rorladning);
    unset($vnr);
    }
}


// My database table:
mysql> SELECT * FROM rorladning;
+------------+-------------+-------+-------------+--------------+---------+--------------+-------------+
| leverandor | valgt_lager | un_nr | varenavn    | varenr       | dim_mm  |
stk_pa_lager | kg_pa_lager |
+------------+-------------+-------+-------------+--------------+---------+--------------+-------------+
| Orica      | Tengs       | 0081  | Hvit Rør   | ETX1.22X1000 | 22x1000 |
70           | 3.7         |
| Orica      | Tengs       | 0081  | Orange Rør | ETX1.17X460  | 17x460  |
70           | 0.95        |
+------------+-------------+-------+-------------+--------------+---------+--------------+-------------+
2 rows in set (0.00 sec)

mysql>

What I think i am doing wrong is the way I write the php/mysql stuff. What
I want is to store differt values in stk_pa_lager based on the particular
serialnumber. (field varenr).

I will be very thankful if you can tell me what is wrong here and point out
what to do with it.
Thanks for your time.

Karl