Pole arm and radio: what they have in common

1. Step 1. Pole arm — is part of — Planimeter. A lever with a fixed pole.
2. Step 2. Planimeter — is part of — Differential analyser. Wheel-and-disc integrators.
3. Step 3. Differential analyser — has part — Gear. Mechanics.
4. Step 4. Gear — is part of — Cipher machine. Wheels set the cipher.
5. Step 5. Cipher machine — is used in — Military radio. Encryption.
6. Step 6. Military radio — is a kind of — Radio. Radio.

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