There are many examples of three-level digital coding, such as postal code, telephone number, student number, house number, license plate number, ID number and so on.

1, postal code:

Postal code usually consists of Arabic numerals, which represents the special code of the post office that delivers mail, and is also the communication code between residents and units within the delivery range of the post office. Postal code is a special code for postal communication to realize mail sorting, and it is a necessary tool to realize postal modernization. The ultimate goal is to improve the speed and accuracy of your letter delivery.

2. Telephone number:

The telephone number is the number set by the telephone management department for the telephone. Generally, it consists of 7-8 digits (mobile phone number is 1 1 digit), with 5-6 digits in the early stage. The designated number set by enterprises, organizations, factories, mines and institutions for internal communication such as fixed telephones or mobile phones is generally 4-8 digits in length. It is also equivalent to the number and name of each mobile phone.

3. Student number:

Student number refers to a number assigned to each student by the school. In order to facilitate the management of students, generally everyone's student number will not be repeated, and the number will generally contain information such as year and class.

4. License plate number:

License plate number is a number plate to identify the identity of the vehicle. It consists of Chinese characters, English letters and numbers, and is issued by the vehicle management office. The license plate number is as important to a car as the ID number is to a person. For example, the license plate is a car from Guangzhou, Guangdong Province, where Guangdong stands for Guangdong Province, A stands for Guangzhou City, and Guangdong A is the license plate number of Guangzhou City.

5. ID number:

Identity number is a kind of characteristic combination code, which consists of 17 digit digital ontology code and digital check code. The serial code is the distribution code of the police station under the jurisdiction of the county and district government. Every police station has a serial number of 10, such as "000-009" or "060-069", where odd numbers are male codes and even numbers are female codes. If there are more than two people on the same day of the same year, the second, third, fourth and fifth allocation codes will be postponed.