public static function Ttut1($tt1, $tt2, $dt, &$ut11, &$ut12) {
    $dtd;

    /* Result, safeguarding precision. */
    $dtd = $dt / DAYSEC;
    if ($tt1 > $tt2) {
      $ut11 = $tt1;
      $ut12 = $tt2 - $dtd;
    }
    else {
      $ut11 = $tt1 - $dtd;
      $ut12 = $tt2;
    }

    /* Status (always OK). */
    return 0;
  }