Mathematics · a Light

A Samarkand mathematician held the record for pi for 180 years

In 1424, working at Ulugh Beg's observatory in Samarkand, Jamshid al-Kashi wrote a short treatise on the circumference of the circle. Using a polygon of more than eight hundred million sides, he calculated two pi correct to sixteen decimal places, and explained why he had gone that far: he wanted the error in a circle the size of the known universe to be less than the width of a horse's hair. Nobody improved on his figure for about 180 years, until Ludolph van Ceulen in the Netherlands. Al-Kashi also set out decimal fractions systematically in his Key to Arithmetic three years later, and gave an iterative method for solving cubic equations.

Al-Kashi · Samarkand, 1424 CE