This final volume in the Charles Babbage Institute Reprint series brings to light an extremely rare German account of the calculating machine industry in the first quarter of this century when the use of office machines became common in American and European business, government, and science. Ernst Martin wrote Die Rechenmaschinen to address the issues and questions that the public had raised about the many calculating devices that were appearing on the market in the early 1920s. His little book is, in fact, a developmental history of calculating machines in catalog form - invaluable for collectors of old machines. The introduction describes the seven major types of machines that had been produced by 1925. The corpus of the book consists of a running list of specific calculating machines, arranged by the date the device was first patented or produced.