We celebrate the life of Simon Stevin tomorrow on October 3, the day of the founding of the University of Leiden (1574). Stevin's exact birthday is unknown.
Stevin entered the University at the age of 35, which is rather old for a student in mathematics, engineering, finance, and navigation. Yet he developed the skills to publish and teach in all of these areas. In mathematics we especially remember Stevin as the man who developed and promoted the use of decimals, i.e., decimal fractions.
Stevin summarized his work on popularizing decimal fractions in his introduction to De Thiende (The Tenth, 1585) as follows:
"It teaches the easy performance of all reckonings, computations, and accounts, without broken numbers (common fractions), which can happen in man's business, in such sort as that the four principles of arithmetic, namely addition, subtraction, muliplication, and division, by whole numbers may satisfy these effects."