Human Computer

Summary

For more than two centuries, a computer was a person. The word named a job, not a machine: someone who computed, who sat with paper, pen, tables of logarithms, and later a mechanical calculator, and ground through the arithmetic that astronomy, navigation, ballistics, and engineering demanded. The job was old by the 1700s, when nations needed star tables to find longitude at sea, and it was still being advertised in the 1950s, when the work was firing artillery and launching rockets.

The great projects ran on human computers organized like factories. Nevil Maskelyne's Nautical Almanac, first issued for 1767, was calculated by a dispersed network of computers and comparers working from their homes across England. After the French Revolution, Gaspard de Prony organized hundreds of workers into a three-tier hierarchy to grind out vast logarithmic and trigonometric tables, boasting that he could manufacture logarithms as one manufactures pins. The model was division of labor applied to arithmetic.

Over the nineteenth and twentieth centuries the role was steadily feminized. At the Harvard College Observatory from the 1880s, Edward Pickering hired a corps of women, the Harvard Computers, to classify stars from photographic plates; among them Williamina Fleming, Annie Jump Cannon, and Henrietta Swan Leavitt made discoveries that reshaped astronomy. During the Second World War, women computed artillery firing tables at Aberdeen, and six of them went on to program ENIAC. At NACA and NASA, the West Area Computers, including Katherine Johnson, Dorothy Vaughan, and Mary Jackson, did the mathematics of flight and spaceflight.

The electronic computer, built in part to do exactly this work, took both the work and the name. ENIAC was completed in 1945; through the late 1950s and 1960s, machines like IBM's mainframes absorbed the calculation. By around 1970 the human computer as a job had effectively ended, but unlike most vanished trades the people did not simply disappear. Many became programmers, mathematicians, and engineers; the title they had held migrated to the machine that replaced them, which is why we still call it a computer.

Decline Timeline

The Work

The human computer's tools were paper, ruled forms, books of mathematical tables, and arithmetic. From the eighteenth century the standard instruments were tables of logarithms and trigonometric functions, which turned multiplication into addition; by the late nineteenth and twentieth centuries computers also used mechanical calculators, hand-cranked and later electric machines like the Marchant, Friden, and Monroe, that could multiply and divide. The work was performed to a fixed procedure: a senior figure broke a problem into a long sequence of simple operations, and the computers executed them, line after line, recording intermediate results on standardized sheets.

Accuracy was the entire point, and the systems were built to enforce it. Maskelyne's Nautical Almanac had each computation done independently by two computers and then checked by a third person, a comparer, so errors would show up as disagreements. De Prony's project, inspired by Adam Smith's account of the division of labor, used a small group of eminent mathematicians to choose the formulas, a middle tier to prepare the procedures, and a large bottom tier of workers, some reportedly hairdressers left unemployed by the Revolution, to do nothing but add and subtract.

The people who did the work changed over time, and so did its status. Early computers were often men or boys; increasingly, and especially in the twentieth century, they were women, hired in part because they could be paid less than men for work that demanded patience, precision, and stamina rather than formal credentials. At Harvard, at Aberdeen, at Langley, rooms of women worked through identical sheets of figures, sometimes for years on a single survey of the sky or a single set of trajectory tables, their names rarely attached to the results.

The Disruption

The disruption came from a machine designed to do the computers' job faster and without fatigue. The decisive step was electronic: ENIAC, the Electronic Numerical Integrator and Computer, was built during the Second World War to calculate artillery firing tables, the very work that human computers at Aberdeen Proving Ground were doing by hand, and was completed in 1945. Tellingly, the people first assigned to operate and program it were themselves human computers, including six women who devised how to make the machine produce trajectories.

The transition was not instantaneous. Early electronic computers were rare, costly, and balky, and through the late 1940s and 1950s human computers continued to work alongside them, often checking the machines' output by hand. At NACA's Langley laboratory and then NASA, the human computing pools persisted into the 1950s and early 1960s; when an IBM electronic computer was brought in to calculate John Glenn's 1962 orbital flight, Glenn reportedly asked that Katherine Johnson verify the machine's numbers before he would fly.

Through the 1960s the economics inverted. As mainframes such as the IBM 700 and 7000 series spread through laboratories, universities, and aerospace, the electronic machine became faster, cheaper per calculation, and more reliable than a room of people, and the human pools were disbanded or converted into programming and analysis groups. By around 1970 the job called computer, in the old human sense, had effectively ceased to exist; the word now meant the machine.

What Killed It

Legacy

The human computer is the rare obsolete trade whose name outlived it by attaching to its successor. We say computer today and mean a machine, but for most of the word's history it meant a worker, usually anonymous, increasingly a woman, doing the patient arithmetic on which navigation, astronomy, war, and spaceflight depended. The machine did not just take the job; it took the title.

The transformation was unusually humane as trades-deaths go. Where the pinboy had only speed to sell, the human computer had genuine mathematical and procedural skill, and that skill was precisely what the new machines needed. The same people who had been displaced wrote the programs, ran the operations, and founded the disciplines of computing. The disruption did not destroy a workforce so much as promote it, at least for those allowed through the door.

That qualifier matters. The recovered history of the Harvard Computers and of NASA's West Area Computers, the latter doing identical work under racial segregation, is also a record of how much skilled labor by women, and by Black women in particular, was done without recognition or credit. The legacy of the human computer is therefore double: a technical lineage that runs straight into the device on every desk, and a social reckoning with who actually did the calculating that built the modern world.

Lessons

References

• Harvard Computers Wikipedia
• When the Computer Wore a Skirt: Langley's Computers, 1935-1970 NASA
• Hidden Figures and Human Computers National Air and Space Museum, Smithsonian Institution
• Gaspard de Prony MacTutor History of Mathematics, University of St Andrews
• The Women Behind ENIAC IEEE Spectrum