Intercom and railway track: what they have in common

1. Step 1. Intercom — has part — Electromagnet. An electromagnetic lock.
2. Step 2. Electromagnet — is part of — Electrical telegraph. Morse’s receiver.
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.

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