Fable
The grain gate in the mill that adjusts its own gap
At the foot of the mountain, the mill had two old grain gates. After the grain came in, one gate decided how much to release, and the other decided which chute it would go down. In the past, the miller only opened the gates according to fixed settings, and when the wheat was uniform, the flour was ground consistently.
There were more and more new grain varieties. Some were dry, some wet, some had large grains, and some had broken husks. Fixed settings either clogged the slot or released too forcefully, heating the millstone. Every day the apprentice could only ask: open wider, or close it a bit.
The apprentice first opened the gate wider. Output went up, but so did the bad powder; then he closed the gate smaller, and the powder became finer, but the speed slowed to the point of queuing. Simply adjusting it larger or smaller could not solve the differences among grain types, and once the rainy season came, the old method became even less stable.
The old miller made a linked gate. One gate first sensed the state of the grain, and the other gate decided how much would pass based on that state. The suitable portion was amplified, and the unsuitable portion was suppressed, so wet grain no longer rushed into the millstones all at once.
At first everyone found it too complicated. The first version of the linked gate also had flaws—it reacted too slowly to grain with husks and still got stuck. The old miller adjusted the gate spring and crank arm so that the side sensing the grain was neither overly sensitive nor sluggish.
After several consecutive rainy seasons, the linked gate became more stable across wet grain, dry grain, and mixed grain, and the stone mill also overheated less. The miller also discovered that the linked gate was most useful in the busiest middle section. The inlet handled receiving grain, the outlet handled discharging flour, and the middle section determined how the grains were processed into a more useful form.
Later, new mills adopted a similar structure. It didn't add an extra groove to the mill, but taught grooves of the same size to filter and amplify. The old miller said that a good mechanism sometimes doesn't rely on piling on more wood, but on gating: amplify what should be amplified, suppress what should be suppressed.
Later the apprentice learned to look at the gate gap, not just the size of the millstone. For the same groove, whether there is an adjustable gate makes the flour output completely different. The mill also had fewer quarrels: when encountering new grain, first see which part should be enlarged and which part suppressed, then decide whether to rebuild the machine. Later, during maintenance, the apprentice also first checked whether the gate control opened and closed according to the grain's nature, and then whether the millstone itself needed replacing.