The first digit of a film number indicates the type of film. For example, a 1 indicates that the film is black and white, a 2 indicates that it is color negative, and a 3 indicates that it is color positive.
The second and third digits of a film number indicate the emulsion number. The emulsion number is a unique number assigned to each type of film emulsion. For example, Kodak Portra 400 has the emulsion number 220.
The fourth and fifth digits of a film number indicate the expiration date. The expiration date is the last day that the film can be used before it starts to deteriorate. For example, a film with the expiration date 1224 would expire on December 24, 2024.
The final digit of a film number is a check digit. The check digit is used to verify that the other digits in the film number are correct.
Film numbers are important because they help to ensure that film is used correctly. For example, a photographer would not want to use expired film, as this would produce poor results. Film numbers also help photographers to identify different types of film, so that they can choose the right film for the job.