Mainspring and rolling mill: what they have in common

1. Step 1. Mainspring — is part of — Gramophone. A spring drive.
2. Step 2. Gramophone — evolved from — Phonograph. A flat disc instead of a cylinder.
3. Step 3. Phonograph — is made of — Tin. The recording is on tin foil.
4. Step 4. Tin — is material for — Model railway. The first models were tinplate.
5. Step 5. Model railway — uses — Railway track. It runs on rails.
6. Step 6. Railway track — uses — Rolling mill. Rails are rolled.

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