Military radio battery pack and gutenberg printing press: what they have in common

1. Step 1. Military radio battery pack — is part of — Military radio. Power.
2. Step 2. Military radio — uses — Cipher machine. Encryption.
3. Step 3. Cipher machine — has part — Keyboard. A keyboard.
4. Step 4. Keyboard — is part of — Linotype. A keyboard.
5. Step 5. Linotype — evolved from — Movable type. Mechanized typesetting.
6. Step 6. Movable type — is part of — Gutenberg printing press. Text is set from metal type.

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