Infrared thermometer and railway semaphore: what they have in common

1. Step 1. Infrared thermometer — uses — Infrared radiation. The infrared radiation of a body.
2. Step 2. Infrared radiation — is used in — Remote control. An infrared signal.
3. Step 3. Remote control — has part — LED. An infrared LED.
4. Step 4. LED — is part of — Traffic light. LEDs.
5. Step 5. Traffic light — evolved from — Railway semaphore. The first traffic light was a railway-style semaphore.

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