Chemical reaction and joystick: what they have in common

1. Step 1. Chemical reaction — is used in — Litmus. Colour from acidity.
2. Step 2. Litmus — evolved into — pH meter. A replacement for indicators.
3. Step 3. pH meter — has part — Amplifier. It amplifies the weak signal of the electrode.
4. Step 4. Amplifier — is part of — Electric guitar. An amplifier.
5. Step 5. Electric guitar — has part — Potentiometer. The volume and tone knobs on an electric guitar are potentiometers.
6. Step 6. Potentiometer — is used in — Joystick. Position is read with potentiometers.

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