Calendar hanging clip and oil lamp: what they have in common

1. Step 1. Calendar hanging clip — is part of — Wall calendar. A spring or a clip.
2. Step 2. Wall calendar — uses — Gutenberg printing press. Printing.
3. Step 3. Gutenberg printing press — has part — Movable type. Text is set from metal type.
4. Step 4. Movable type — is made of — Clay. Bi Sheng’s type was made of fired clay.
5. Step 5. Clay — is material for — Oil lamp. Later — clay ones.

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