Dorr Felt patents the comptometer

Background. Dorr Eugene Felt, an American inventor, developed the comptometer, recognized as the first commercially successful key-driven mechanical calculator. The machine operated by adding or subtracting key values to an accumulator instantly upon pressing. This design challenged the arithmometer's dominance, though initial sales were slow. Felt's work stemmed from earlier key-driven concepts, including Thomas Hill's 1857 patent and Pascal's 1642 Pascaline.

Development and Partnership. Felt completed an early version soon after New Year's Day 1885. Robert Tarrant, a Chicago workshop owner, provided resources including a $6 weekly salary and $5,000 for construction. Felt finished the first practical machine on October 5, 1886. By September 1887, eight production units existed. Felt and Tarrant signed a partnership contract on November 28, 1887, later incorporating as Felt & Tarrant Manufacturing Company in January 1889.

Patents and Production. The first two patents were granted on July 19, 1887, and October 11, 1887. Early machines, called "woodies," used wooden boxes, making them lighter but fragile. Approximately 6,500 such machines were built between 1887 and 1903. Felt filed seven patents in the first ten years, continually improving the design. The comptometer name became a generic term for this class of calculating machines.