Alkaline battery and joystick: what they have in common

1. Step 1. Alkaline battery — is part of — Electronic calculator. A calculator runs on a battery, sometimes on a tiny solar panel.
2. Step 2. Electronic calculator — evolved into — Microprocessor. The Intel 4004 was designed for a Busicom calculator.
3. Step 3. Microprocessor — is part of — Game console. A processor.
4. Step 4. Game console — has part — Gamepad. A gamepad.
5. Step 5. Gamepad — evolved from — Joystick. A game controller.

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