Wall calendar and greenhouse: what they have in common

1. Step 1. Wall calendar — uses — Gutenberg printing press. Printing.
2. Step 2. Gutenberg printing press — has part — Movable type. Text is set from metal type.
3. Step 3. Movable type — evolved into — Linotype. Mechanized typesetting.
4. Step 4. Linotype — uses — Casting. It casts a line of type in metal.
5. Step 5. Casting — is used in — Window glass. The panes were cast in moulds.
6. Step 6. Window glass — is part of — Greenhouse. It lets light in and holds heat.

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