A single stroke of ink in 1675 still shows up in every calculus class.

On October 29, 1675, the German thinker Gottfried Wilhelm Leibniz, then working in Paris, wrote a stretched letter S in his private notes. It stood for "summa," Latin for sum, and he used it to describe adding up infinitely small pieces.

That long S became the integral sign. Leibniz's notation for calculus proved so clear that scientists and engineers still use it to calculate areas, motion and change.

Do you think good notation matters as much as the discovery itself?

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