This is a vintage Addometer mechanical calculator, likely manufactured by the Reliable Typewriter & Adding Machine Company of Chicago, Illinois.Functionality: This portable adding machine was used for performing basic addition and subtraction by dialing numbers with a stylus.Production: The Addometer was produced in the United States from approximately the 1900s through the 1960s before being replaced by electronic calculators.Features: The device typically features an 11-inch ruler on the top edge, and some models include color-coded dials for working with currency.Reset Mechanism: A sliding lever on the side allows all dials to be reset back to zero.