Photocopier and hollerith tabulator: what they have in common

1. Step 1. Photocopier — has part — Lens. Optics.
2. Step 2. Lens — is used in — Optical telegraph. Signals were read through telescopes.
3. Step 3. Optical telegraph — evolved into — Electrical telegraph. The electrical telegraph replaced semaphore lines.
4. Step 4. Electrical telegraph — has part — Relay. Relays boosted the signal on long lines.
5. Step 5. Relay — is part of — Hollerith tabulator. Relays controlled the sorting box.

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