Simon Stevin (Dutch: [ˈsimɔn steːˈvɪn]; 1548–1620), sometimes called Stevinus, was a Flemish mathematician, scientist and music theorist.

[3] Simon Stevin's mother, Cathelijne (or Catelyne), was the daughter of a wealthy family from Ypres; her father Hubert was a poorter of Bruges.

Based on references in his work "Wisconstighe Ghedaechtenissen" (Mathematical Memoirs), it has been inferred that he must have moved first to Antwerp where he began his career as a merchant's clerk.

Later the Calvinists seized power in many Flemish cities and incarcerated Catholic clerics and secular governors supportive of the Spanish rulers.

[7] Stevin's work in the waterstaet involved improvements to the sluices and spillways to control flooding, exercises in hydraulic engineering.

Windmills were already in use to pump the water out but in Van de Molens (On mills), he suggested improvements including ideas that the wheels should move slowly with a better system for meshing of the gear teeth.

In The First Book of the Elements of the Art of Weighing, The second part: Of the propositions [The Properties of Oblique Weights], Page 41, Theorem XI, Proposition XIX,[10] he derived the condition for the balance of forces on inclined planes using a diagram with a "wreath" containing evenly spaced round masses resting on the planes of a triangular prism (see the illustration on the side).

As noted by E. J. Dijksterhuis, Stevin's proof of the equilibrium on an inclined plane can be faulted for using perpetual motion to imply a reductio ad absurdum.

[2]: 54 He demonstrated the resolution of forces before Pierre Varignon, which had not been remarked previously, even though it is a simple consequence of the law of their composition.

[7] Stevin discovered the hydrostatic paradox, which states that the pressure in a liquid is independent of the shape of the vessel and the area of the base, but depends solely on its height.

[11][12] The first mention of equal temperament related to the twelfth root of two in the West appeared in Simon Stevin's unfinished manuscript Van de Spiegheling der singconst (ca 1605) published posthumously three hundred years later in 1884;[13] however, due to insufficient accuracy of his calculation, many of the numbers (for string length) he obtained were off by one or two units from the correct values.

Double-entry bookkeeping may have been known to Stevin, as he was a clerk in Antwerp in his younger years, either practically or via the medium of the works of Italian authors such as Luca Pacioli and Gerolamo Cardano.

[15][7] Stevin wrote a 35-page booklet called De Thiende ("the art of tenths"), first published in Dutch in 1585 and translated into French as La Disme.

Al-Kashi's book, Key to Arithmetic, was written at the beginning of the 15th century and was the stimulus for the systematic application of decimals to whole numbers and fractions thereof.

He felt that this innovation was so significant, that he declared the universal introduction of decimal coinage, measures and weights to be merely a question of time.

The point separating the integers from the decimal fractions seems to be the invention of Bartholomaeus Pitiscus, in whose trigonometrical tables (1612) it occurs, and it was accepted by John Napier in his logarithmic papers (1614 and 1619).

That Stevin intended these encircled numerals to denote mere exponents is clear from the fact that he employed the same symbol for powers of algebraic quantities.

[7] Stevin wrote on other scientific subjects – for instance optics, geography, astronomy – and a number of his writings were translated into Latin by W. Snellius (Willebrord Snell).

The work brought to the western world for the first time a general solution of the quadratic equation, originally documented nearly a millennium previously by Brahmagupta in India.

According to Van der Waerden, Stevin eliminated "the classical restriction of 'numbers' to integers (Euclid) or to rational fractions (Diophantos)...the real numbers formed a continuum.

[19] A recent study attributes a greater role to Stevin in developing the real numbers than has been acknowledged by Weierstrass's followers.

Following his life, Belgium and the city of Bruges have continued to name places, statues and other topics in honor of Stevin Amongst others, he published: