Monroe was a businessman whose interest in mechanics made him well aware of the limitations of the calculating machines of the time. The adding and listing machines used by the banking houses were large and cumbersome, and were generally limited to adding and totalising only. The key-driven Comptometers were capable of very fast and accurate addition and could also do multiplication and division, but they required a skilled operator to get the best results. The rotary calculators based on the pin-wheel and stepped-drum mechanisms were relatively straightforward in multiplication and division, but their setting mechanisms (using sliders and rotary dials) were far too slow and error-prone to be useful in adding long columns of numbers.

Monroe saw a need for a simple and portable calculator for business applications, which could be used with minimal training, and which would perform all four arithmetic functions with equal ease. He recognised that Baldwin's latest design had the potential to combine the rapid setting of the key-driven machines with the full arithmetic capabilities of the rotary calculators, and a partnership was formed to develop the machine for production. Monroe himself is said to have played a significant part in the technical development, and his name appears as inventor on several of the subsequent patents.

The Monroe Calculating Machine Company was formed in New York in 1912. The firm acquired premi
The history of the Monroe company
The Monroe Calculator Company is founded in 1912 by businessman Jay R. Monroe and Frank Baldwin, the inventer of his pinwheel technology. The company turned out to be a leading maker of adding and calculator machines.

Baldwin was an architect by profession, but like many 19th-century men, he was also a prolific inventor who held patents in several unrelated fields. He developed the first pinwheel calculator in 1872-3, and continued to work on a variety of calculator mechanisms throughout his long and productive life. The beginnings of what was later to become the Monroe mechanism can be clearly seen in his US Patent 890888 of 1908, designed when he was already into his seventies. Baldwin died in 1925, just short of his 87th birthday.
ses in Orange NJ (formerly occupied by the Pike Adding Machine Company), and the first Monroe "High Speed Adding Calculator" entered full-scale production in 1914. Edgar Phinney continued the development of the machine until his departure in about 1920. George Chase joined Monroe in 1917, and soon became Chief Engineer. Chase led the technical development for over thirty years, through models K, L, and M and into the MonroMatic range, and was still active in the company into the 1950s. Herman Gang continued the development through the N series MonroMatics and on into the 1960s. The Monroe product range covered an enormous variety of styles and features, from basic hand-cranked units to high-speed motor-driven machines with multiple registers and fully-automatic multiplication and division. Although still slower than the Comptometer in adding long columns of figures, the machines excelled in any application that required more than just repeated addition. They found a ready home in business and commercial applications, and were the mainstay of many scientific and engineering offices from the 1920s until the early 1970s.

To complement the non-printing rotary calculators, Monroe acquired a range of full-keyboard adding and listing machines from the Gardner company in the early 1930s. The Gardner printing calculators were developed into a successful line of bookkeeping and accounting machines through the 1940s and 50s. Under the post-war European reconstruction plan (the Marshall Plan) Monroe established new factories in Holland and Italy, and re-sold a range of 10-key adding machines built by Olympia in Germany. Manufactures like Nisa and Brunsviga used Moroe's "Split Stepped Drum" technology at their machines to.

The Monroe company was acquired by Litton Industries in 1958, and became part of Litton's business systems group. Calculator development and production continued into the 1960s, but by the 1970s the Monroe name was being applied to general office equipment and photocopiers from other sources in the Litton group. The Monroe company has changed hands several times since, but still exists, and is still selling electronic calculators under the Monroe brand.

(Text is addapted from John Wolff)