$req = 'select * from `'.$psql.'sonde_data` WHERE id="'.$s_name.'" AND boot="'.$boot.'" order by `cpt` DESC LIMIT '.$cpt2.',1';
$req = mysql_query($req, $connexion);
while($data_sonde = mysql_fetch_object($req));
      {
               /*
                * taille graph = 400
                * début graphe = 31
                * fin graphe   = 431 
                */
                $val = (197-($data_sonde->valeur*2));
                imagesetpixel($im, $cpt, $val, $couleur[5]);

                $cpt--;
                $cpt2++;
       }