Mary Clem

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Mary Clem
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Nevada, Western Iowa, USA
Died1979(1979-00-00) (aged 73–74)
CitizenshipUnited States of America
Alma materIowa State College
  • Mathematician
  • Human computer
Notable work
zero check

Mary Clem (1905 - 1979) was an American mathematician and human computer who invented the “zero check”.


Early life:

She was born in the small town of Nevada, which is located in Western Iowa. She completed her high school degree and found employment for several years with the Iowa State Highway Commission and Iowa State College as a computing clerk, auditing clerk, and bookkeeper [1].


In 1931, she joined the Mathematics Statistical Service of the Mathematics Department of Iowa State College to work as a human computer under the supervision of George Snedecor.[2]. Although she complained that mathematics was her poorest subject in high school, she was entirely fascinated with figures and data. Most of her work was done via punch cards, both creating formulas and cards, and running accuracy checks on them. She invented the “zero check” while working in Snedecor’s lab. The “zero check” is a sum that should equal zero if all other numbers had been correctly calculated [2]. These sums helped check for errors in computing algorithms. Mary believes that her lack of training as a mathematician is what made her notice these sums, as they had often been overlooked by others [2]. In 1940, Mary was advanced to be technician and chief statistical clerk in charge of the Computing Service of the Statistical Laboratory. In 1962, she transferred to the new Computation Center at Iowa State University [1]

Later in life:

She went on the 2nd Allied Mission to Greece in 1946 as a junior statistician, and there she observed the elections.[1]. In 1952, she was a statistical consultant to the Atomic Bomb Casualty Commission in Hiroshima Japan [1]


  • Homeyer, Paul G.; Clem, Mary A.; and Federer, Walter T. (1947) "Punched card and calculating machine methods for analyzing lattice experiments including lattice squares and the cubic lattice," Iowa Agriculture and Home Economics Experiment Station Research Bulletin: Vol. 28 : No. 347 , Article 1. [3]

Primary sources

  • Clem, Mary. “Interview with Mary Clem by Uta Merzbach,” June 27, 1969, SMITHSONIAN.
  • “Mary Clem,” Iowa State University Faculty Newsletter , vol. 25, no. 20, February 2nd, 1979.


  1. 1.0 1.1 1.2 1.3 "Mary A. Clem". Retrieved 2020-09-21.
  2. 2.0 2.1 2.2 Grier, David Alan (2007). When Computers Were Human. USA: Princeton University Press. pp. 159–174. ISBN 978-0-691-13382-9.
  3. Homeyer, Paul G., Clem, Mary A. and Federer, Walter T (1947). "Punched card and calculating machine methods for analyzing lattice experiments including lattice squares and the cubic lattice". Iowa Agriculture and Home Economics Experiment Station Research Bulletin. Vol. 28 : No. 347: Article 1. {{cite journal}}: |volume= has extra text (help)CS1 maint: multiple names: authors list (link)

External links

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