Photochemical reaction and electronic calculator: what they have in common

1. Step 1. Photochemical reaction — is used in — Silver halide. It is decomposed by light.
2. Step 2. Silver halide — is made of — Silver. A silver salt.
3. Step 3. Silver — is material for — pH meter. The internal electrode is silver chloride.
4. Step 4. pH meter — has part — Liquid-crystal display. An indicator.
5. Step 5. Liquid-crystal display — is part of — Electronic calculator. An LCD display.

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