Yoke and programmable logic controller: what they have in common

1. Step 1. Yoke — is used in — Plough. It was pulled by oxen in a yoke.
2. Step 2. Plough — is used in — Crop rotation. The three-field system with a heavy plough.
3. Step 3. Crop rotation — evolved into — Mineral fertilizer. Fertilizers solved the problem of fertility that crop rotation used to solve.
4. Step 4. Mineral fertilizer — uses — Sulfuric acid. Superphosphate is made with sulfuric acid.
5. Step 5. Sulfuric acid — is used in — Chemical plant. The first chemical plants produced sulfuric acid and soda.
6. Step 6. Chemical plant — has part — Programmable logic controller. Process control automation.

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