Pocket watch and petri dish: what they have in common

1. Step 1. Pocket watch — evolved into — Marine chronometer. Harrison moved from large clocks to the pocket-sized H4.
2. Step 2. Marine chronometer — has part — Bimetallic strip. Harrison invented the bimetal strip to compensate for temperature.
3. Step 3. Bimetallic strip — is part of — Electric kettle. Automatic switch-off when the water boils.
4. Step 4. Electric kettle — evolved from — Kettle. A kettle with a heater.
5. Step 5. Kettle — has part — Pot lid. A cap.
6. Step 6. Pot lid — is part of — Petri dish. A cap.

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