Stamp punching has three functions. First, when you sell stamps, you don't tear the stamps themselves, so it's convenient to tear the whole stamps into individual sheets. Second, it is convenient to count the number of stamps. Thirdly, the perforation forms a decorative "boundary" around the stamp screen, which increases the aesthetic feeling of the stamp.
When the world's first stamp "Black Penny" came out, it had no perforations and was inconvenient to use. You must cut them one by one with scissors. It was not until 1854 that perforated stamps appeared in Britain.
The perforation density of stamps is measured by the number of perforations, and it is expressed by the number of perforations within 20 mm. The perforation degree is one of the important basis for distinguishing the authenticity of stamps, distinguishing different versions and printing times.