Sliding middle scale and archimedes’ screw: what they have in common

1. Step 1. Sliding middle scale — is part of — Slide rule. A movable scale.
2. Step 2. Slide rule — is a kind of — Computing device. An analogue calculator.
3. Step 3. Computing device — includes — Tide-predicting machine. An analogue calculator.
4. Step 4. Tide-predicting machine — has part — Pulley. Pulleys add up the harmonics.
5. Step 5. Pulley — is a kind of — Simple machine. A pulley is a simple machine.
6. Step 6. Simple machine — includes — Archimedes’ screw. A classic example of using the screw.

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