Convection and hollerith tabulator: what they have in common

1. Step 1. Convection — is used in — Hot air balloon. Hot air rises and fills the canopy.
2. Step 2. Hot air balloon — is made of — Paper. It was lined with paper on the inside.
3. Step 3. Paper — is material for — Punched card. Punched cards are stiff card.
4. Step 4. Punched card — is used in — Hollerith tabulator. The 1890 census data was encoded on punched cards.

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