Revolution counter and davy lamp: what they have in common

1. Step 1. Revolution counter — is part of — Anemometer. It converts revolutions into speed.
2. Step 2. Anemometer — is part of — Weather station. An anemometer.
3. Step 3. Weather station — has part — Hygrometer. A hygrometer.
4. Step 4. Hygrometer — is made of — Plant fibre. Humidity was shown by a fibre that changed length.
5. Step 5. Plant fibre — is material for — Wick. A wick is twisted from plant fibres.
6. Step 6. Wick — is part of — Davy lamp. A wick.

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