Culture medium (agar) and hollerith tabulator: what they have in common

1. Step 1. Culture medium (agar) — is used in — Sewage treatment plant. Waste water is cleaned by activated sludge — bacteria.
2. Step 2. Sewage treatment plant — is made of — Concrete. The tanks are concrete.
3. Step 3. Concrete — is material for — Maglev. The guideway is concrete.
4. Step 4. Maglev — uses — Electromagnetism. Electromagnets hold and move the train.
5. Step 5. Electromagnetism — is used in — Hollerith tabulator. The counters click with electromagnets.

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