Abacus and pneumatic tube: what they have in common

1. Step 1. Abacus — is made of — Stone. Counting was done with pebbles — the Latin calculus.
2. Step 2. Stone — is material for — Ice house. Ice houses were built of stone and sunk into the ground.
3. Step 3. Ice house — evolved into — Refrigerator. The refrigerator replaced natural ice.
4. Step 4. Refrigerator — has part — Compressor. A compressor with an electric motor.
5. Step 5. Compressor — is part of — Pneumatic tube. A pressure or vacuum blower.

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