Stethoscope and watt steam engine: what they have in common

1. Step 1. Stethoscope — is used in — Blood pressure monitor. Listening for the Korotkov sounds.
2. Step 2. 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.
3. Step 3. Manometer — is part of — Boiler. The gauge on a boiler shows the steam pressure — without it the boiler could explode.
4. Step 4. Boiler — is part of — Watt steam engine. The boiler supplies steam.

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