In the early 1600s, astronomers and navigators faced one specific problem: multiplying very large numbers. Calculating a planet's position or a ship's course required multiplying multi-digit numbers together, often hundreds of times in a single computation. Each calculation took hours. Errors were common — and at sea, errors were dangerous.

John Napier (NAY-pee-er), a Scottish mathematician working in Edinburgh, Scotland, spent twenty years solving this problem. He noticed a pattern: to multiply two numbers, you can add their exponents instead. He called these exponents logarithms, from the Greek words for "ratio" and "number." In 1614 CE, he published a complete table of them in his Mirifici Logarithmorum Canonis Descriptio ("A Description of the Wonderful Canon of Logarithms").

English mathematician Henry Briggs traveled to Edinburgh to meet Napier. Together they redesigned the tables using base 10 — the system that became standard across Europe. For the next 350 years, sailors used logarithm tables to navigate oceans and astronomers used them to calculate orbits. Engineers used them to design machines. When the first electronic calculators appeared in the 1970s, logarithm tables finally went out of use. The notation you write today — log₁₀(x) — came directly from the work Napier published in 1614 CE.