Why is photography 35 frames called 135? What does 1 mean?

1In the 1920s, Leica Company of Germany developed a camera that can shoot 35mm film (36×24mm), which is also called "Leica Roll". Later, more and more cameras were produced in various factories around the world to shoot 35mm film, so the name "Leica Roll" was no longer appropriate, so it was changed to "35mm film" according to the width of the film. It was not until 1950s that it was used in film boxes in order to distinguish 35mm film for cameras from 35mm bulk film. Later, it was recognized that the 35mm film was called 135 film, and the camera of 135 film was called 135 camera.