Liquid-crystal display and stone tool: what they have in common

1. Step 1. Liquid-crystal display — is part of — pH meter. An indicator.
2. Step 2. pH meter — is made of — Silver. The internal electrode is silver chloride.
3. Step 3. Silver — is material for — Syringe. Early needles were silver.
4. Step 4. Syringe — has part — Needle. A hollow needle.
5. Step 5. Needle — evolved from — Stone tool. Bone needles with an eye are part of the Palaeolithic toolkit.

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