Chainsaw and electrical telegraph: what they have in common

1. Step 1. Chainsaw — has part — Roller chain. The cutting chain is a roller chain with teeth.
2. Step 2. Roller chain — is part of — Roller coaster. A chain lift.
3. Step 3. Roller coaster — uses — Railway track. Rails.
4. Step 4. Railway track — inspired — Time zones. Introduced because of railway timetables.
5. Step 5. Time zones — uses — Electrical telegraph. Synchronizing time by telegraph.

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