public static function Tttai($tt1, $tt2, &$tai1, &$tai2) {
    /* TT minus TAI (days). */
    $dtat = TTMTAI / DAYSEC;

    /* Result, safeguarding precision. */
    if ($tt1 > $tt2) {
      $tai1 = $tt1;
      $tai2 = $tt2 - $dtat;
    }
    else {
      $tai1 = $tt1 - $dtat;
      $tai2 = $tt2;
    }

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