Gristmill and tunnelling shield: what they have in common

1. Step 1. Gristmill — uses — Grain. A mill grinds grain.
2. Step 2. Grain — is used in — Grain elevator. It stores and transfers grain.
3. Step 3. Grain elevator — has part — Bucket elevator. A bucket lift.
4. Step 4. Bucket elevator — works like — Conveyor belt. A conveyor with buckets that lifts goods vertically.
5. Step 5. Conveyor belt — is part of — Tunnel boring machine. Spoil is removed by a conveyor.
6. Step 6. Tunnel boring machine — evolved from — Tunnelling shield. A development of the tunnelling shield.

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