🧲Pull systems

In a push system each step makes what the plan says and sends it downstream whether or not anyone is ready for it. In a pull system a step makes only what the next step has just taken. Make what was taken, and nothing else.

Ohno describes it in 📕 Toyota Production System and says he took the idea from American supermarkets: the shelf is refilled because a customer emptied it. The signal that travels back upstream is a card, the 🔤 Kanban.

• Push fails by overproduction, which he ranks as the worst waste because it hides the others.
• Pull fails when the downstream step does not know what it needs.

Example from work: the Exceptions Inbox pushes every row at a dispatcher because the system happens to know about it. Pull would be sending what they asked for, when they asked.

Often confused with: just-in-time as no stock at all. Pull limits stock. It does not abolish it.

Notes: 📖 Ohno on waste and pull. My claim, with its condition: 💎 Pull beats push when the downstream step knows more.