Arithmetic · a Light

He moved arithmetic off the dust board and onto paper

In Damascus in 952 a mathematician known as al-Uqlidisi wrote a book on calculating with the Indian numerals. Reckoning was then done on a takht, a board spread with fine dust, where each step was wiped out as the next was written. He argued for ink and paper instead, partly because the dust board was the tool of street fortune tellers and carried their reputation, and partly because on paper the working stays where you can check it. In the same book he uses a mark to separate a whole number from the fraction following it, which is the earliest known use of a decimal fraction. Al-Kashi set decimal fractions out systematically in 1427, and Simon Stevin made them ordinary in Europe in 1585.

Al-Uqlidisi · Damascus, 952 CE