Snap fastener and electronic calculator: what they have in common

1. Step 1. Snap fastener — has part — Spring. A spring ring.
2. Step 2. Spring — is part of — Kitchen scale. The load stretches a spring.
3. Step 3. Kitchen scale — is a kind of — Balance scale. Scales.
4. Step 4. Balance scale — evolved into — Electronic scales. Electronic scales.
5. Step 5. Electronic scales — has part — Liquid-crystal display. The reading is on an LCD.
6. Step 6. Liquid-crystal display — is part of — Electronic calculator. An LCD display.

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