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[2] Eusebio Huélamo, "Algunos Recuerdos del Cálculo Mecánico." DYNA, October, 1995, Spain.

[2] Robert K. Otnes, "Sliding Bar Calculators," ETCetera, No. 11, June, 1990.

[3] Peggy Aldrich Kidwell, "American Adders: Circles and Bands." ETCetera, No. 31, June, 1995.

[4] Ernst Martin, "The Calculating Machines." The MIT Press, Cambridge, Massachusetts, 1992. English translation made by Peggy Aldrich Kidwell and Michael R. Williams, from the original "Die Rechenmaschinen" published in 1925 by Johannes Meyer, Pappenheim.

[5] J.A.V. Turck, "Origin of Modern Calculating Machines." The Western Society of Engineers, Chicago, 1921.

[6] Bryan Morgan, "Total to Date, The Evolution of the Adding Machine: The Story of Burroughs." Burroughs Adding Machine Limited, London. 19??

[7] E. Darby, "It all adds up - The Growth of Victor Comptometer Corporation." Chicago, IL. Victor Comptometer Corporation, 1968.

[8] Hans Blohm, Stafford Beer, David Suzuki, "Pebbles to Computers, The Thread." Oxford University Press, Toronto, 1986.

[9] Erwin Tomash, "An Interview with Curt Herzstark. 10-11 September 1987, Nendeln, Liechtenstein." Charles Babbage Institute, University of Minnesota, Minneapolis, Minn.

[10] Earl Swartzlander, "Generations of Calculators." IEEE Annals of the History of Computing, Vol. 17, No. 3, 1995, pp. 75-77.

[11] Earl Swartzlander , "The Victor Adding Machine." IEEE Annals of the History of Computing, Vol. 17, No. 4, 1995, pp. 4.

[12] Daniel Lewin. Personal notes on mechanical calculators.

[13] Wassén, Henry, 'The Odhner history : An illustrated chronicle of "a machine to count on". In commemoration of the 100th anniversary of W. T. Odhner's birth in 1845', Göteborg, Original-Odhner ab, 1951, 67 pages.

[14] Nigel Tout. Notes on Comptometers submitted to Erez Kaplan's mailing list (June/2000)

[Internet Sources]