The check code is the last digit of a group of numbers, which is obtained from the previous number through some operation to verify the correctness of the group of numbers. Common verification codes include the last digit of the People's Republic of China resident ID card, the last digit of the ISBN number, and so on.
A code with a verification code is composed of an ontology code and a verification code (such as an organization code). The ontology code is the number representing the encoded object, and the verification code is the number appended to the ontology code to verify the accuracy of the ontology code in the input process. Each ontology code can only have one check code, and the check code is obtained by the specified mathematical relationship.