Johannes Widmann’s (1460-1498) Behende und hübsche Rechnung auf allen Kauffmanschafften (1489) is a seminal work in the history of commercial arithmetic. Written for merchants, it provides practical methods for calculations in trade, finance, and double-entry bookkeeping. The book is particularly notable for its clear explanations of the rule of three, profit calculations, and interest rates. Widmann's work helped standardize mathematical techniques essential for economic transactions in the early modern period. Beyond its practical applications, the book made significant contributions to algebra. Widmann introduced the modern use of the plus (+) and minus (−) signs, which later became fundamental in mathematical notation. His algebraic approach laid the groundwork for later European mathematicians. While not a purely theoretical text, it bridges the gap between arithmetic and algebraic reasoning. The clarity and accessibility of his methods made mathematics more practical for a broader audience. Widmann’s work remains an important historical milestone in mathematical development. It reflects the growing role of mathematics in commerce and finance during the Renaissance. This book is essential reading for historians of mathematics and economic history. Online at: Württembergische Landesbibliothek See also: Luca Pacioli, 1494 See also: Balance sheet