Measuring wheel and zip: what they have in common

1. Step 1. Measuring wheel — is part of — Planimeter. A counting wheel integrates the area.
2. Step 2. Planimeter — has part — Wheel. A measuring wheel computes the area.
3. Step 3. Wheel — is part of — Siege tower. On wheels.
4. Step 4. Siege tower — is made of — Leather. They were covered with raw hides against fire.
5. Step 5. Leather — is material for — Bag. Leather.
6. Step 6. Bag — has part — Zip. A zip.

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