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.