Tracer arm and knife: what they have in common

1. Step 1. Tracer arm — is part of — Planimeter. A stylus traces the outline.
2. Step 2. Planimeter — has part — Wheel. A measuring wheel computes the area.
3. Step 3. Wheel — is part of — Michaux velocipede. The Michaux velocipede had two wooden wheels, with pedals on the front one.
4. Step 4. Michaux velocipede — has part — Crank. Cranks on the wheel axle.
5. Step 5. Crank — is part of — Meat grinder. A handle.
6. Step 6. Meat grinder — has part — Knife. A cross-shaped blade.

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