The term "computer", in use from the early 17th century (the first known written reference dates from 1613), meant "one who computes": a person performing mathematical calculations, before electronic computers became commercially available. "The human computer is supposed to be following fixed rules; he has no authority to deviate from them in any detail." (Turing, 1950) Teams of people were frequently used to undertake long and often tedious calculations; the work was divided so that this could be done in parallel.
Since the end of the 20th century, the term "human computer" has also been applied to individuals with prodigious powers of mental arithmetic, also known as mental calculators. The first time the term "Computer" appeared in the New York Times was in May 2, 1892; the ad by the US Civil Service Commission stated:
- "A Computer Wanted. [...] The examination will include the subjects of algebra, geometry, trigonometry, and astronomy."
Origins in astronomy 
The approach was taken for astronomical and other complex calculations. Perhaps the first example of organized human computing was by the Frenchman Alexis Claude Clairaut (1713–1765), when he divided the computation to determine timing of the return of Halley's Comet with two colleagues, Joseph Lalande and Nicole-Reine Lepaute. For some men, being a computer was a temporary position until they moved on to greater advancements. For women the occupation was generally closed, but this changed in the late 19th century with Edward Charles Pickering. His group was at times termed "Pickering's Harem."
Many of the women astronomers from this era were computers with possibly the best known being Henrietta Swan Leavitt.
Florence Cushman was another of the Harvard University computers from 1888 onward. Among her best known works was A Catalogue of 16,300 Stars Observed with the 12-inch Meridian Photometer. She also worked with Annie Jump Cannon.
Female computers normally earned half of what a male counterpart would.
The Indian mathematician Radhanath Sikdar was employed as a "computer" for the Great Trigonometric Survey of India in 1840. It was he who first identified and calculated the height of the world's highest mountain, later called Mount Everest.
Wartime computing and the invention of electronic computing 
Human computers have played integral roles in the World War II war effort in the United States, and because of the depletion of the male labor force due to the draft, many computers during World War II were women, frequently with degrees in mathematics. In the Manhattan Project, human computers, working with a variety of mechanical aids, assisted numerical studies of the complex formulas related to nuclear fission. Because the six people responsible for setting up problems on the ENIAC (the premiere general-purpose electronic digital computer built at the University of Pennsylvania during World War II) were drafted from a corps of human computers, the world's first professional computer programmers were women, paving the way for careers in data processing as socially acceptable for women in an era of gender roles. These six computers-turned-computer-programmers were Kay McNulty, Betty Snyder, Marlyn Wescoff, Ruth Lichterman, Betty Jean Jennings, and Fran Bilas.
Following World War II, the NACA used human computers in flight research to transcribe raw data from celluloid film and oscillograph paper and then, using slide rules and electric calculators, reduce it to standard engineering units.
Use of the term to refer to humans in human-based computation 
The term "human computer" has been recently used by a group of researchers who refer to their work as "human computation" (Law, 2011) In this usage, "human computer" refers to activities of humans in the context of human-based computation (HBC). This usage is questionable for the following reason. HBC is a computational technique where a machine outsources certain (not necessarily algorithmic) tasks to humans. In fact, most of the time humans in the context of HBC are not provided with a sequence of exact steps that needs to be executed to yield an answer. HBC is agnostic about how humans solve the problem. This is why the term outsourcing is used in the definition. The use of humans as "human computers" in the context of HBC is very rare. It makes little sense (beyond testing) simply because automatic computers are faster than humans at executing known algorithms and less error-prone.
See also 
- Turing, Alan Mathison (1950). Computing machinery and intelligence. Mind, 59, 433-460.
- Grier, David Alan, The Human Computer and the Birth of the Information Age, Joseph Henry Lecture, Philosophical Society of Washington, May 11, 2001.
- Grier, David Alan, When Computers Were Human, Princeton University Press, 2005. ISBN 0-691-09157-9.
- Campbell-Kelly, Martin, The Origin of Computing, Scientific American, September 2009.
- Mark Wolverton, "Girl Computers", American Heritage, Fall 2011
- Edith Law, Luis von Ahn, "Human Computation", Morgan and Claypool publishers, 2011