Before Computers Were Machines, They Were Women. Here Are Six Places Where Human Computers Built Modern Science

From AT&T to NASA, women working as computers performed the calculations that made modern science possible. In the early 1900s, computing joined teaching and nursing as one of the few careers open to college-educated women, and it opened doors that few other professions could

New York City native Sallie Pero lived with her family while she attended Barnard College, the all-women liberal arts school affiliated with Columbia University. Only 16 when she began her studies in 1909, Pero excelled at math and athletics. Between field hockey, basketball and baseball, Pero played a sport every season. Physical activity paired well with her studies. When she graduated in 1913, Pero received Barnard’s Kohn Mathematics Prize and went on to complete a master’s program in mathematics at Columbia University. She started out as a substitute teacher in New York City schools but left teaching to work as a computer at American Telephone and Telegraph (AT&T) in 1915.

In the first decades of the 1900s, computing was emerging as a potential career, in addition to teaching and nursing, for women graduating from college. In fact, for scientifically inclined women, such as Pero (1893-1981), working as a computer opened the door to a career in scientific research.

Computer Was a Job Description

Historically, all computers were human. Computers performed mathematical calculations in accounting and record keeping for government and financial institutions, navigation on the ocean, and engineering public works. Computing was a job requiring mathematical skills and a tolerance for repetitive activity. Although computation had taken place throughout history, the demand for it accelerated with the Industrial Revolution. Manufacturing, commerce, scientific research, engineering and the development of new technology, as well as compiling and analyzing large groups of data all heavily relied on human computers.

Human computers used available tools such as mathematical tables, slide rules and calculating machines. They were also among the first users and operators of new electronic computers, although relatively few were involved in their development. The first electronic computers came into use during the decade following World War II. Their rapid development was galvanized by the enormous war-time demand for complex calculations. Hand computation and teams of human computers were common until the 1980s when the availability of electronic computers finally caught up to the demand. During this time, computers began mastering coding languages and transitioning to computer programming. Women’s participation in computing occupations peaked in the late 1980s before a 20-year decline, despite continued growth in other STEM professions.

The history of women and human computing is just beginning to be fully explored. Researchers and historians know that the need for computing was widespread and that women did much of this work, but finding the individual histories of the women involved is challenging. Sometimes it is a matter of knowing where to look. In many cases, the names of these women are part of human resource records that have not been preserved or digitized. Other times, you need to know what you're looking for to recognize the evidence when you find it, as is the case with the misspelled and somewhat illegible “Computter” listed as Sallie Pero’s occupation in the 1915 New York City census shown above.

Read about the following six places where women worked as human computers and think about where you could look for human computers in your own community.

1. Harvard College Observatory

Family connections, a woman benefactor and graduates trained in astronomy at nearby women’s colleges all contributed to the notable pool of women computers at the Harvard College Observatory. Computers took the observations made by astronomers while working with the telescope and translated or “reduced” those descriptions into data that could be analyzed. Since computing took place indoors during the day and was less physically active than stellar observation, it fit the era's expectations for women's behavior and was considered an acceptable way for women to work in astronomy at Harvard at a time when only men attended the school. Harvard’s first woman computer, Anna Winlock (1857-1904), the daughter of a former director of the observatory, was one of many women with family connections who came to work at the observatory. A backlog of unreduced observations motivated Edward Charles Pickering to employ a reliable group of woman computers soon after he became director of the Harvard College Observatory in 1877. Recent graduates from Vassar, Wellesley and Radcliffe sought professional opportunities at the observatory.

Astrophotography became another area of women’s expertise. The women became the caretakers and decoders of the thousands of newly created glass-plate photographs taken with the aid of the telescope. The glass plate collection was financially supported by Anna Palmer Draper (1839-1914), another woman connected to the observatory through her deceased husband. Significantly, 216 women have been identified with work on the collection of 400,000 glass plate photographs. Unfortunately, family connections and a woman benefactor did not prevent low wages for the women computers. For some, the opportunity to work in astronomy outweighed their concern for money. Outstanding women computers, such as Annie Jump Cannon (1863-1941) and Henrietta Leavitt (1868-1921), made remarkable discoveries working with the glass plates and went on to distinguished careers in astronomy. But most of the women did not advance beyond the role of computer.

 2. AT&T and Bell Telephone Laboratories

AT&T employed women as human computers to aid its engineers in developing new systems and equipment for telephone, radio and later television. Although their effort contributed to the widespread success of the company, only a few of these women are remembered by name. Pero was one of them. Performing complicated math related to telephone traffic collision, Pero was soon recognized as a valuable industrial mathematician. She transitioned from “computer” to “engineer” when she joined the transmission engineering unit in 1919. Known as Sallie P. Mead after her 1924 marriage, she applied for her first of six patents that year. Mead was the first woman at AT&T to hold a patent and publish a technical report in the Bell System Technical Journal. In 1933, Mead was part of a team that made a breakthrough discovery in waveguide technology that is still used in radar systems today.

3. Works Progress Administration’s Mathematical Tables Project

The U.S. government’s Works Progress Administration (WPA) organized the Mathematical Tables Project in 1938 to produce standard mathematical tables by which all WPA project data could be analyzed. Reference tables or charts showing the results of calculations for specific mathematical functions such as exponents or trigonometric values had long been used to speed up computation. Gertrude Blanch (1897-1996), a Jewish immigrant from Poland, became the project’s mathematical director. Despite holding a doctorate in algebraic geometry from Cornell University, she had not previously worked as a mathematician. However, she drew upon 20 years of experience in business to develop her systems of production and assure the accuracy of the tables. While most experts were skeptical of using unemployed workers in a computing laboratory, Blanch transformed the work of computing by devising a novel division of labor that foreshadowed the methods of machine computers. Complex calculations were broken down into basic steps that could be performed simultaneously by a pool of individuals possessing only fundamental skills.

Under Blanch’s supervision, the Mathematical Tables Project produced 28 volumes that were eventually published by Columbia University Press. The Mathematical Tables Project was the foundation of a major reference produced by the National Bureau of Standards. Two of Blanch’s colleagues from the Mathematical Tables Project, Milton Abramowitz and Irene Stegun, edited the Handbook of Mathematical Functions, with Stegun overseeing its publication in 1964. Blanch contributed to the volume, which supported hand computation in research labs for 20 years before the availability of computers matched the demand. The Handbook was one of the most widely circulated books of scientific literature from the 1900s, selling over a million copies.

4. The U.S. Army’s Philadelphia Computing Section

The U.S. Army’s Ballistics Research Laboratory at the Aberdeen Proving Grounds in Maryland used a combination of hand and machine calculation to create the firing tables for the Army’s ballistic weapons. Soldiers in the field used the tables to set trajectories, drop points, elevation angles and muzzle velocities for each weapon depending on variables in temperature, air density, wind drift and target position. Hand computing a single trajectory occupied 30-40 hours of work. A portion of these calculations were performed on a differential analyzer, a computing machine that greatly reduced the required time.

During World War II, the volume of essential calculations quickly exceeded the capacity of the Ballistics Research Laboratory. The Army organized a second operation utilizing the differential analyzer located at the Moore School of Engineering at the University of Pennsylvania and recruited women computers to do the work previously done by men. The women of the Philadelphia Computing Section joined hundreds of other women recruited by the government and military to meet the computing demands during the war.

Kathleen McNulty (1921-2006), one of the operators of the differential analyzer pictured above, discovered an affinity for math in high school. She graduated with a degree in mathematics from Chestnut Hill College for Women in Philadelphia in June 1942. Soon afterward, she and her classmate Frances Bilas (1922-2012) responded to a civil service posting in the Philadelphia Inquirer recruiting women with degrees in mathematics. At the Philadelphia Computing Section, McNulty and Bilas received additional training and practice before being assigned to work on the differential analyzer. McNulty was eventually promoted to supervising calculations on the analyzer.

In June 1945, McNulty and Bilas became part of a team of six women computers tasked with operating the ENIAC, an early electronic computer that was being developed by the Army at the Moore School of Engineering. They operated the ENIAC by physically setting switches and configuring cables between different components for each calculation. Together the women developed efficient and reliable operating techniques that became fundamental to computer programming.

5. NASA’s Langley Memorial Aeronautical Laboratory

Langley Memorial Aeronautical Laboratory near Hampton, Virginia, created its first female computer pool in 1935. Langley was the main research center for the National Advisory Committee for Aeronautics, the precursor to NASA. As the facility grew to meet the technological demands of World War II and the subsequent space race, so did its need for computing. In common across the different divisions of aeronautic research was the need for computers to extract data from readings taken during experiments, run calculations to analyze the data and then plot the results on graphs. Aside from pencils and paper, the only tools used to do the work were basic calculating machines and slide rules.

Dorothy Vaughan (1910-2008) more than doubled her salary as a math teacher at a high school in Farmville, Virginia, when she became part of Langley’s West Computing Area during World War II. Jim Crow laws in Virginia required that Vaughan and her colleagues work separately from their white counterparts. However, Langley’s engineers quickly recognized the competency of the African American women who formed West Area Computing Unit and frequently requested Vaughan when they had difficult calculating assignments. Although Vaughan led the West Area Computing Unit from 1949 to 1958, she did not remain in management after the West Computers joined the desegregated Analysis and Computation Division in 1958. The role of human computers began to change as electronic computers became part of the work process. Vaughan became an expert in Fortran, the computer language used in engineering simulations. She helped other women transition from human computer to programmer before retiring in 1971.

6. Jet Propulsion Laboratory at the California Institute of Technology

Women computers were part of the workflow of the Jet Propulsion Laboratory (JPL), at the California Institute of Technology from the beginning. In 1939, Barbara Canright (1919-1997) was the first woman recruited to manage the complicated math involved in the physics of rocket science. Before Canright left the JPL in 1943 to have a baby, three other women had been hired as computers. One of those women, Macie Roberts (1898-1991), became the supervisor of the computer group and cultivated a close-knit team of highly motivated women. Her successor, Helen Ling (b. 1928) created a career path that supported women who wanted to work while raising a family as well as those who wanted advance in the aerospace industry.

The JPL computing group utilized the most up-to-date machine technologies to aid their work, enabling the women to develop expertise in computer programming alongside their other abilities. In time, the women were writing many of the programs involved in the missions to outer space. Around 1970, the job title “computer” was replaced with “engineer” at the JPL, and all new hires were required to have college degrees in engineering. Since the number of women with engineering degrees was still small, Ling began recruiting talented women as programmers and encouraged them to grow within the organization by getting advanced degrees in engineering.

Do You Know a Human Computer?

Help us shine a light on women’s contributions by telling us about a human computer in your community. Use this form to share her story.

Further Reading:

• Ashcraft, Catherine, Brad McLain, and Elizabeth Eger, “Women in Computing: What Are the Numbers?” in Women in Tech: The Facts. National Center for Women & Information Technology (2016): 6-18.
• Coxson, Greg and William Haloupek. “Sallie P. Mead: An Industrial Mathematician in the Early 20th Century." Society for Industrial and Applied Mathematics News, June 15, 2022.
• Grier, David Alan. When Computers Were Human. Princeton University Press, 2005.
• Holt, Nathalia. Rise of the Rocket Girls: The Women Who Propelled Us, From Missiles to the Moon to Mars. Little, Brown and Company, 2016.
• Light, Jennifer S. “When Computers Were Women.” Technology and Culture 40, no. 3 (1999): 455–83.
• McLennan, Sarah and Mary Gainer. “When the Computer Wore a Skirt: Langley’s Computers, 1935-1970.” NASA History News & Notes, 29.1 (First Quarter 2012): 25-32.
• Zrull, Lindsay Smith. “Women in Glass: Women at the Harvard Observatory during the Era of Astronomical Glass Plate Photography, 1875-1975.” Journal for the History of Astronomy 52.2 (2021): 115-146.

Related Reading:

• Maria Mitchell: America’s First Woman Astronomer and Mentor to Women in Science
• New Partnership Illuminates Hidden Record of NASA’s Human Computers
• Five Women Who Shaped Our Understanding of Space
• Hazel Fellows and the Women Who Made the Apollo Spacesuits
• New Quarter Honors Vera Rubin, Astronomer Who Revealed the Universe’s Hidden Mass