$sqlq = "SELECT kjoring FROM oko WHERE kjoring!='' ORDER BY logdate DESC LIMIT 2";

    if ( array_key_exists( 'field' , $out ) ) {
    $sqlq = $sqlq . " where field = '" . $out['field'] . "'" ;
  }
  $conn = new mysqli($servername, $username, $password, $dbname);

  $result = mysqli_query( $conn , $sqlq );

  if ( $result->num_rows  > 0 ) {
  while($row = mysqli_fetch_array($result)) {

  $km1 = $row[0];
  $km2 = $row[1];

$km0 = $km1 - $km2 ;
  }
}

echo $km0 ;