Author(s):
Frank J. Swetz (The Pennsylvania State University)
In 1527, Petrus Apianus (1495-1552), also known as Peter Apian, was appointed to a mathematics position at the University of Ingolstadt. In the same year, Apianus published a reckoning book directed at the needs of commerce: Ein newe und wolgegründte underweisung aller Kauffmans Rechnung in dreien Büchern (A new and well-founded instruction of all merchant arithmetic).
The images below come from a later edition, published in Frankfurt in 1537. The title page depicts a busy scene of bookkeepers computing.

A didactical diagram is used to illustrate number relationships.

The images above are provided courtesy of Columbia University Libraries.
Index to Mathematical Treasures
Frank J. Swetz (The Pennsylvania State University), "Mathematical Treasure: Commercial Arithmetic by Petrus Apianus," Convergence (June 2018)