Balance pans and gas lamp: what they have in common

1. Step 1. Balance pans — is part of — Balance scale. For the load and weights.
2. Step 2. Balance scale — evolved into — Electronic scales. Electronic scales.
3. Step 3. Electronic scales — has part — Liquid-crystal display. The reading is on an LCD.
4. Step 4. Liquid-crystal display — has part — LED. LED backlighting.
5. Step 5. LED — is part of — Street light. LEDs.
6. Step 6. Street light — evolved from — Gas lamp. Gas lamps.

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