Oxygen concentrator and gutenberg printing press: what they have in common

1. Step 1. Oxygen concentrator — has part — Valve. They switch the columns.
2. Step 2. Valve — is part of — Watt steam engine. A slide valve distributes the steam.
3. Step 3. Watt steam engine — is part of — Rotary printing press. The first rotary presses were steam-driven.
4. Step 4. Rotary printing press — evolved from — Gutenberg printing press. Cylinders instead of a flat press.

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