Used as part of a Just-In-Time production operation where components and sub-assemblies are produced based upon notification of demand from a subsequent operation. Historically, Kanban has been a physical notification such as a card (kanban cards) or even an empty hopper or tote sent up the line to the previous operation. Kanban is actually a simplistic means of both signaling the need for inventory as well as controlling the inventory levels (by limiting kanban cards or containers).