De Thiende
This article reads like a review rather than an encyclopedic description of the subject. (July 2012)

De Thiende is a landmark publication authored by Simon Stevin in the 16th century. It was the first book in the western world to use decimal fractions. Although he did not invent the practice and notation system was complex, his pamphlet established the decimal system as a practice in mathematics.^{[1]}
Simon Stevin's biography
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The Princeton Companion to Mathematics provides the following biographical information about Simon Stevin:^{[2]}
"The Flemish mathematician and engineer Simon Stevin is remembered for his study of decimal fractions. Although he was not the first to use decimal fractions (they are found in the work of the tenthcentury Islamic mathematician alUqlidisi), it was his tract De Thiende (“The tenth”), published in 1585 and translated into English (as Disme: The Art of Tenths, or Decimall Arithmetike Teaching ) in 1608, that led to their widespread adoption in Europe. Stevin, however, did not use the notation we use today. He drew circles around the exponents of the powers of one tenth: thus he wrote 7.3486 as 7 3^{(1)} 4^{(2)} 8^{(3)} 6^{(4)}. In De Thiende Stevin not only demonstrated how decimal fractions could be used but also advocated that a decimal system should be used for weights and measures and for coinage."
Importance
The importance of Stevin's book De Thiende was expressed in The Princeton Companion to Mathematics:^{[2]}
"The idea of extending the decimal placevalue system to include fractions was discovered by several mathematicians. The most influential of these was Simon Stevin, a Flemish mathematician and engineer who popularized the system in a booklet called De Thiende (“The tenth”), first published in 1585. By extending place value to tenths, hundredths, and so on, Stevin created the system we still use today. More importantly, he explained how it simplified calculations that involved fractions, and gave many practical applications. The cover page, in fact, announces that the book is for astrologers, surveyors, measurers of tapestries."
References
External links
 Disme: the Art of Tenths, Or, Decimall Arithmetike (1608) by Simon Stevin, Tr. Robert Norton, @GoogleBooks
 La Thiende at britannica.com