Digital blood pressure monitor and davy lamp: what they have in common

1. Step 1. Digital blood pressure monitor — evolved from — Blood pressure monitor. An automatic blood pressure monitor.
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 — Newcomen engine. Steam from the boiler.
5. Step 5. Newcomen engine — uses — Coal mine. Pumping water out of mines.
6. Step 6. Coal mine — uses — Davy lamp. Protection against methane explosions.

Open Evothings