Space station and saw: what they have in common

1. Step 1. Space station — has part — Solar panel. Power comes from solar panels.
2. Step 2. Solar panel — is part of — Electronic calculator. Many run on a solar cell.
3. Step 3. Electronic calculator — evolved from — Arithmometer. Electronics replaced mechanics.
4. Step 4. Arithmometer — has part — Crank. The handle for adding and subtracting.
5. Step 5. Crank — is part of — Sawmill. A crank turns the wheel’s rotation into the stroke of the saw.
6. Step 6. Sawmill — uses — Saw. The cutting tool is a saw.

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