Prefabrication and telephone: what they have in common

1. Step 1. Prefabrication — is used in — Panel building. Assembled from panels.
2. Step 2. Panel building — has part — Elevator. Lifts.
3. Step 3. Elevator — has part — Elevator safety brake. Otis’s safety brakes.
4. Step 4. Elevator safety brake — has part — Spring. Springs throw out the catches when the rope goes slack.
5. Step 5. Spring — is part of — Rotary dial. A return spring.
6. Step 6. Rotary dial — is part of — Telephone. A dial.

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