Alidade sighting rule and refrigerator: what they have in common

1. Step 1. Alidade sighting rule — is part of — Astrolabe. A sighting rule.
2. Step 2. Astrolabe — evolved into — Quadrant. A simplified angle gauge.
3. Step 3. Quadrant — has part — Plumb bob. A plumb line shows the vertical.
4. Step 4. Plumb bob — is made of — Stone. The bob of a plumb line is stone or copper.
5. Step 5. Stone — is material for — Ice house. Ice houses were built of stone and sunk into the ground.
6. Step 6. Ice house — evolved into — Refrigerator. The refrigerator replaced natural ice.

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