Vacuum tube and smart meter: what they have in common

1. Step 1. Vacuum tube — includes — Magnetron. An electron vacuum device.
2. Step 2. Magnetron — has part — Permanent magnet. A magnet makes the electrons spiral.
3. Step 3. Permanent magnet — is part of — Electricity meter. A braking magnet.
4. Step 4. Electricity meter — evolved into — Smart meter. A digital meter.

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