Minesweeper and hollerith tabulator: what they have in common

1. Step 1. Minesweeper — has part — Sonar. Searching for mines.
2. Step 2. Sonar — works like — Ultrasound scanner. A medical sonar: the same echo principle.
3. Step 3. Ultrasound scanner — has part — Monitor. A screen.
4. Step 4. Monitor — has part — Cathode-ray tube. The first monitors were CRTs.
5. Step 5. Cathode-ray tube — uses — Electromagnetism. The beam is deflected by a magnetic field.
6. Step 6. Electromagnetism — is used in — Hollerith tabulator. The counters click with electromagnets.

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