Metric system and knife: what they have in common

1. Step 1. Metric system — uses — Hindu–Arabic numerals. Decimal multiples.
2. Step 2. Hindu–Arabic numerals — works like — Abacus. Positional counting with beads.
3. Step 3. Abacus — is made of — Stone. Counting was done with pebbles — the Latin calculus.
4. Step 4. Stone — is material for — Adze. The blade of an adze was ground from stone.
5. Step 5. Adze — evolved from — Stone tool. Neolithic adzes were stone.
6. Step 6. Stone tool — evolved into — Knife. The first knives were stone flakes.

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