Ruler body and pneumatic tube: what they have in common

1. Step 1. Ruler body — is part of — Ruler. Wood, metal or plastic.
2. Step 2. Ruler — has part — Measurement scale. Marked graduations.
3. Step 3. Measurement scale — is part of — Barometer. Millimetres of mercury.
4. Step 4. Barometer — uses — Vacuum. The Torricellian vacuum above the mercury.
5. Step 5. Vacuum — is used in — Hyperloop (concept). A vacuum in the tube.
6. Step 6. Hyperloop (concept) — was inspired by — Pneumatic tube. Capsules in a tube — pneumatic post for people.

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