Elevator and telephone: what they have in common

1. Step 1. Elevator — has part — Elevator safety brake. Otis’s safety brakes.
2. Step 2. Elevator safety brake — has part — Spring. Springs throw out the catches when the rope goes slack.
3. Step 3. Spring — is part of — Rotary dial. A return spring.
4. Step 4. Rotary dial — is part of — Telephone. A dial.

Open Evothings