Planimeter and barrel: what they have in common

1. Step 1. Planimeter — has part — Wheel. A measuring wheel computes the area.
2. Step 2. Wheel — is used in — Windlass. A windlass is a wheel and axle used as a simple machine.
3. Step 3. Windlass — is part of — Drawbridge. Raised with a windlass.
4. Step 4. Drawbridge — is a kind of — Bridge. A bridge.
5. Step 5. Bridge — has part — Arch. Stone bridges were built as arches.
6. Step 6. Arch — works like — Barrel. Staves squeezed by hoops hold their shape by the same compression as the stones of an arch.

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