code: private boolean checkGrVatId(final String pvatId) {
      final int checkSum = pvatId.charAt(10) - '0';
      final int sum = (pvatId.charAt(2) - '0') * 256 + (pvatId.charAt(3) - '0') * 128
          + (pvatId.charAt(4) - '0') * 64 + (pvatId.charAt(5) - '0') * 32
          + (pvatId.charAt(6) - '0') * 16 + (pvatId.charAt(7) - '0') * 8
          + (pvatId.charAt(8) - '0') * 4 + (pvatId.charAt(9) - '0') * 2;
      int calculatedCheckSum = sum % MODULO_11;
      if (calculatedCheckSum > 9) {
        calculatedCheckSum = 0;
      }
      return checkSum == calculatedCheckSum;
    }
docs: check the VAT identification number, country version for Greece.
  
  @param pvatId vat id to check
  @return true if checksum is ok