Odhner Arithmometer, also known as the Odhner Calculator, was a mechanical calculator invented by Swedish engineer Willgodt Odhner in the late 19th century. The device was widely used in offices and businesses for performing mathematical calculations before the advent of electronic calculators. Synonyms for the Odhner Arithmometer include mechanical calculator, adding machine, computation machine, and mechanical adding device. It used a series of gears and cylinders to perform mathematical operations and displayed results on a mechanical readout system. These devices were popular for their durability and accuracy, and they played a critical role in the development of mathematics and engineering.