Semaphore signal arms and oil well: what they have in common

1. Step 1. Semaphore signal arms — is part of — Optical telegraph. The positions of the arms encode characters.
2. Step 2. Optical telegraph — evolved into — Electrical telegraph. The electrical telegraph replaced semaphore lines.
3. Step 3. Electrical telegraph — is used in — Time zones. Synchronizing time by telegraph.
4. Step 4. Time zones — was inspired by — Railway track. Introduced because of railway timetables.
5. Step 5. Railway track — is made of — Wrought iron. Then — wrought iron.
6. Step 6. Wrought iron — is material for — Oil well. The casing pipes are iron.

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