Pinwheel with sliding teeth and boiler: what they have in common

1. Step 1. Pinwheel with sliding teeth — is part of — Arithmometer. A wheel with retractable teeth sets a digit.
2. Step 2. Arithmometer — has part — Crank. The handle for adding and subtracting.
3. Step 3. Crank — is part of — Ice cream maker. A handle.
4. Step 4. Ice cream maker — uses — Latent heat. Ice with salt draws away heat.
5. Step 5. Latent heat — is used in — Boiler. Evaporation needs latent heat.

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