Fable
Before each brick leaves the kiln, it first passes the same row of rulers
Several workshops in Hongyao Town fired city bricks together. In the past, each workshop first prepared clay, changed molds, and adjusted the fire in its own yard, and only delivered the bricks to the central kiln at month's end. Once the city wall failed inspection, no one knew whose clay or which firing had ruined the whole batch.
The mayor first added a big month-end inspection. The stricter the inspection, the later the rework; some bricks had already been laid into half a wall, and taking them down was harder than firing them again.
The old kiln worker changed the rules: each household sent a small number of new bricks to the main kiln mouth every day, first passing size gauges, sound tests, water immersion, and pressure tests. Only after passing were they merged into the large batch; if they failed, they were returned to that day's formula and not allowed to be delayed until the end of the month.
Later the town also set up a small section of wall for trial masonry. Only after the bricks on the small wall had endured a night of wind and rain without cracking or seeping were they allowed to be transported to the main wall. If the clay material changed on some day, it would affect only a small section and would not ruin the whole city's project.
At first the workshop found daily inspection a hassle, thinking a month-end check could also catch bad bricks. But a same-day return costs only one kiln, while a month-end return can bring down half a wall. The value of early detection isn't in finding more faults, but in catching errors while they're still small.
Test-building a small wall also once saved a major project. A certain new clay material passed on the scale, but after a rainy night it seeped water. The main kiln stopped using that batch the same day, and the city wall project was delayed by only half a day, rather than investigating only after the main wall cracked.
Later, the workshops actually felt more at ease. Only a small number of new bricks were submitted each day, and mistakes were known the same day; bricks that passed the gauge could be merged into the main kiln faster and sent to the small wall for trial laying. The city wall didn't suddenly grow at month's end — it was continuously added brick by brick after passing the same row of gauges. Later, the wall was built faster and faster, yet rework decreased. Each brick entered the same row of gauges early, and the small wall bore wind and rain on behalf of the main wall. Problems surfaced daily and were handled daily, no longer accumulating into a major collapse at month's end. The workshops also dared to change clay, molds, and fire more frequently, because each change was quickly caught by the same row of gauges.
At first the workshop found it troublesome, but after a few months it became easier instead. Merging in small steps, verifying bricks at any time, and being ready to deliver at any time was more stable than betting on one furnace at month-end. What the assembly line truly saved was the cost of discovering errors late.