Relay and rolling mill: what they have in common

1. Step 1. Relay — is part of — Electrical telegraph. Relays boosted the signal on long lines.
2. Step 2. Electrical telegraph — is used in — Time zones. Synchronizing time by telegraph.
3. Step 3. Time zones — was inspired by — Railway track. Introduced because of railway timetables.
4. Step 4. Railway track — uses — Rolling mill. Rails are rolled.

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