Hourglass and hollerith tabulator: what they have in common

1. Step 1. Hourglass — uses — Gravity flow. Sand pours through under gravity.
2. Step 2. Gravity flow — is used in — Water filter. Water seeps through by gravity.
3. Step 3. Water filter — works like — Paper coffee filter. Filtering a liquid through a porous medium.
4. Step 4. Paper coffee filter — is made of — Paper. Paper.
5. Step 5. Paper — is material for — Punched card. Punched cards are stiff card.
6. Step 6. Punched card — is used in — Hollerith tabulator. The 1890 census data was encoded on punched cards.

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