ÿØÿÛC  ÿØÿÛC  $digit) { if ($index % 2 === 0) { $evenSum += $digit; } else { $oddSum += $digit; } } $tenthDigit = (7 * $evenSum - $oddSum) % 10; $eleventhDigit = ($evenSum + $oddSum + $tenthDigit) % 10; return $tenthDigit . $eleventhDigit; } /** * Checks whether a TCNo has a valid checksum * * @param string $tcNo * * @return bool */ public static function tcNoIsValid($tcNo) { return self::tcNoChecksum(substr($tcNo, 0, -2)) === substr($tcNo, -2, 2); } }