Patent Model of Edmondson's Circular Calculating Machine, 1883

Mechanical calculators used gears, cogs, levers, and rotating drums to solve mathematical problems indirectly. While Edmondson� s Circular Calculator was rugged and reliable, its "stepped drum" system required people to slide plates and levers, making it difficult to master and time-consuming to operate. By the late-19th century, improved adding machines became popular, helping to reduce the common errors of human calculation.