Does a NAC have self error-detecting function?
Yes. Many people suggested to include an extra character to be the error detecting character. Once a miswritten NAC is input, the mail sorting computer can find out the error immediately, which can prevent a local mail from sending to other countries or continents. It is a good idea but will add more burden to people to remember a NAC and have more chance to include errors too. Fortunately, a NAC has already certain self error-detecting function. It is well known that most of the earth surface is covered by oceans where no people live and no country is. Therefore, an international postal zone database can easily supply the information where people do not live. When a wrong NAC is read by a mail sorting computer, if the first or second character in a string of the NAC is wrong, it is most propably within an ocean and the computer can notice it easily. If only the third or fourth character is wrong, it may still represent a location locally and can be corrected easily by the post office
