The primary function of a kanban card is to provide information about production instructions. Kanban cards contain information about where to produce and transport a particular product, when and in what quantity. For information to be useful in making good decisions and in spotting abnormalities, it must be visible.

Keep your kanban cards close to your genbutsu (actual product or actual item). Information in the form of kanban must be attached to actual parts or part containers, making only brief visits to kanban posts or heijunka boards, in order to function as a visual management tool.

When kanban are used correctly, the managers and supervisors on the gemba can gain quite a bit of knowledge about these key factors in shop floor management:

1) What is our open capacity, based on available time versus kanban cards returned?
2) How much inventory do I have in my process?
3) How well is standard work being followed, based on the pace of p-kanbans released to line?
4) How well is the staffing of my process balanced to demand or mix changes?
5) How fast or slow is the status of the downstream process pulling cards?
6) What should we be working on next?

To maintain visual management through a pull system, keep the information (kanban card, cart, or other object) physically together with the genbutsu (actual product). Managing by using production information in the form of a limited number of kanban cards in circulation will allow you to prevent overproduction, know what to work on next, and keep control of your materials.

Another way of thinking about this is that if your system, push or pull, does not allow shop floor management to gain information such as whether the workers are able follow their standard work, this is not a properly functioning kanban system.