The Andon Light (or Stop the line, I want to get off)

One oft-mentioned feature of Lean manufacturing is the andon light or the andon cord. The idea is that any employee on the assembly line who encounters a problem pulls the andon cord, the line is stopped, and the light comes on to indicate where the problem is.

By the way, andon is the Japanese word for paper lantern, which has apparently been generalized to mean any lantern. Here are a couple of good references about the history of andon lanterns:

Although andon lights are frequently mentioned in the Agile development literature, some of their most important points are sometimes glossed over.

In A Study of the Toyota Production System, Shigeo Shingo, an industrial engineer noted in connection with Toyota’s SMED (Single Minute Exchange of Dies) program that reduced setup times for punch presses from many hours to less than a minute, said:

The andon is a visual control that communicates important information and signals the need for immediate action by supervisor. There are some managers who believe that a variety of production problems can be overcome by implementing Toyota’s visual control system. At Toyota, however, the most important issue is not how quickly personnel are alerted to a problem, but what solutions are implemented. Makeshift or temporary measures, although they may restore the operation to normal most quickly, are not appropriate.

The key point is that each time the line is stopped because of the andon, the team strives to make sure that the same error does not happen again. Shingo states this more forcefully when he says “At Toyota, there is only one reason to stop the line—to ensure that it won’t have to stop again.”

The andon lights used by continuous integration teams come close to this philosophy. The light comes on when a build fails, or the automated tests that run as part of the build fail. Everyone on the team stops what they are doing and works on fixing the build.

What is missing sometimes is the idea of making sure that it doesn’t happen again, perhaps by implementing a Poka-yoke solution that will prevent the error from happening again.

When you read about the Toyota production system, what is striking is the commitment to doing whatever it takes to eliminate waste and errors, even at the expense of some short-team pain.

This is difficult to do in a mature company that is trying to adapt to Agile development, because it is a major change, and various departments are not used to working closely together. But it is essential to eliminate waste.


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