Tracker bar and solar panel: what they have in common

1. Step 1. Tracker bar — is part of — Player piano. Holes let air through to the valves.
2. Step 2. Player piano — uses — Program control of a machine. The tune is recorded on a perforated roll.
3. Step 3. Program control of a machine — is used in — Industrial robot. The movements are recorded in a program.
4. Step 4. Industrial robot — is part of — International Space Station. The Canadarm2 robotic arm.
5. Step 5. International Space Station — has part — Solar panel. Solar panels.

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