Felt & Tarrant Comptometer, circa 1945

Mechanical adding machines were indispensable office equipment used before the computer era. These devices were perfected by the American Arithmometer Company in 1886, spurred on by William Seward Burrough's desire to reduce drudgery in clerical arithmetic work. Transistors and electronic desktop calculators displaced adding machines in the 1950s; by the 1970s, microchips reduced calculators to the size of a shirt pocket.