Lighthouse lamp and micrometer: what they have in common

1. Step 1. Lighthouse lamp — is part of — Lighthouse. The lamp: oil, kerosene, then electricity.
2. Step 2. Lighthouse — is part of — Seaport. A lighthouse.
3. Step 3. Seaport — uses — Sailing ship. A port receives ships.
4. Step 4. Sailing ship — has part — Anchor. An anchor.
5. Step 5. Anchor — has part — Shackle. The chain mount.
6. Step 6. Shackle — is part of — Micrometer. A rigid frame.

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