Gunpowder mill and fitness tracker: what they have in common

1. Step 1. Gunpowder mill — has part — Water wheel. The drive.
2. Step 2. Water wheel — is part of — Trip hammer. The shaft was turned by a water wheel.
3. Step 3. Trip hammer — evolved from — Hammer. A trip hammer is a hammer lifted and dropped by a water wheel.
4. Step 4. Hammer — includes — Reflex hammer. A hammer.
5. Step 5. Reflex hammer — is made of — Vulcanized rubber. A rubber head.
6. Step 6. Vulcanized rubber — is material for — Fitness tracker. The strap is silicone.

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