Monroe Mechanical Adding-Calculator
1930s

In 1983 Computer Museum of America started its collection with this artifact.

Frank Stephen Baldwin, 1838-1925, American inventor, began in 1870 to experiment with the design of mechanical calculators. The device was patented and marketed in 1875.

The improved 1875 machine initiated the development of the second fundamental principle in rotary four-rules calculators which became known as "The Baldwin Principle."

Baldwin developed many more calculators during his life. His last model was the forerunner of the Monroe machine.

The Monroe Calculator was used extensively in the 1930's. The Monroe Calculator Company was formed in 1912 and was a pioneer in electric adding machines. Monroe Calculators are STILL sold today through Monroe Systems for Business.

Donor: Reece Franklin, Computer News of San Diego