Blood pressure monitor and steam locomotive: what they have in common

1. Step 1. Blood pressure monitor — evolved from — Manometer. A blood pressure monitor is a manometer connected to a cuff: it measures the air pressure that squeezes the artery.
2. Step 2. Manometer — is part of — Boiler. The gauge on a boiler shows the steam pressure — without it the boiler could explode.
3. Step 3. Boiler — includes — Fire-tube boiler. A boiler.
4. Step 4. Fire-tube boiler — is part of — Stephenson’s Rocket. A multi-tube boiler.
5. Step 5. Stephenson’s Rocket — is a kind of — Steam locomotive. A steam locomotive.

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