Slide rule and plumbing: what they have in common

1. Step 1. Slide rule — is a kind of — Computing device. An analogue calculator.
2. Step 2. Computing device — includes — Astrolabe. An analogue calculator of celestial positions.
3. Step 3. Astrolabe — evolved into — Quadrant. A simplified angle gauge.
4. Step 4. Quadrant — uses — Universal gravitation. The angle is read against a plumb line.
5. Step 5. Universal gravitation — is used in — Water tower. Pressure from height.
6. Step 6. Water tower — is part of — Plumbing. Maintaining pressure.

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