Barcode scanner and pneumatic tube: what they have in common

1. Step 1. Barcode scanner — is part of — Self-checkout. It reads the goods.
2. Step 2. Self-checkout — evolved from — Cash register. A till.
3. Step 3. Cash register — is used in — Supermarket. Tills.
4. Step 4. Supermarket — uses — Refrigerator. Refrigerated displays.
5. Step 5. Refrigerator — has part — Compressor. A compressor with an electric motor.
6. Step 6. Compressor — is part of — Pneumatic tube. A pressure or vacuum blower.

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