Document scanner bar and elevator: what they have in common

1. Step 1. Document scanner bar — is part of — Fax. It reads the sheet line by line.
2. Step 2. Fax — uses — Telephone. Transmission over a telephone line.
3. Step 3. Telephone — has part — Rotary dial. A dial.
4. Step 4. Rotary dial — has part — Spring. A return spring.
5. Step 5. Spring — is part of — Elevator safety brake. Springs throw out the catches when the rope goes slack.
6. Step 6. Elevator safety brake — is part of — Elevator. Otis’s safety brakes.

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