Differential analyser and plough: what they have in common

1. Step 1. Differential analyser — has part — Planimeter. Wheel-and-disc integrators.
2. Step 2. Planimeter — has part — Wheel. A measuring wheel computes the area.
3. Step 3. Wheel — is part of — Stagecoach. On four wheels.
4. Step 4. Stagecoach — uses — Horse collar. It is pulled by horses.
5. Step 5. Horse collar — is used in — Plough. The horse collar made ploughing with horses possible.

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