Jean-Paul Sartre
http://www.teilestore.de/edu/?p=164

Luis Fernandes, "The Abacus, the Art of Calculating with Beads,"
http://www.ee.ryerson.ca:8080/~elf/abacus/

Tomoe Soroban Co. Ltd. "Soroban,"
http://www.soroban.com/index_eng.html

MacTutor, "History of Mathematics archive,"
http://www-groups.dcs.st-and.ac.uk/~history/

Paul E. Dune, "History of Science -Course Notes."
http://dee.csc.liv.ac.uk/~ped/teachadmin/histsci/content.html

David Hicks, "Calculating Machines."
http://www.webcom.com/calc/

Erez Kaplan, "Calculating Machines."
http://www.webcom.com/calc/main.html

David Weil, "Computer Museum of America."
http://www.computer-museum.org

Charles Babbage Institute, "Burroughs Corporation History."
http://www.cbi.umn.edu/burros/burhist.htm

University of Exeter, "The Babbage Pages."
http://www.ex.ac.uk/BABBAGE/welcome.html

Gerold Beckers, "Mechanical Calculators."
http://www.geo.tudelft.nl/mgp/people/gerold/

Ernst-Moritz-Arndt. "Katalog der Rechentechnischen Sammlung des Instituts für Mathematik und Informatik." Universität Greifswald.
http://gryps2.rz.uni-greifswald.de/fakul/mathematics/RTS/

David Wilkins, "The History of Mathematics."
http://www.maths.tcd.ie/pub/HistMath/

David E. Joyce, "History of Mathematics." Clark University
http://aleph0.clarku.edu/~djoyce/mathhist/mathhist.html

Dirk Gfrörer, Martin Hejl. "The History of Computers." Fachhochschule für Technik Esslingen.
http://www-stall.rz.fht-esslingen.de/studentisches/Computer_Geschichte/

Tom ??, "Tom's Calculating Devices."
http://www.groundcntrl.com/slide/troncets.htm

Bruce Flamm, "The Amazing Curta."
http://www2.bath.ac.uk/~masres/calcs/curta.html

Rick Furr , "The CURTA Calculator Page."
http://www.public.usit.net/rfurr/cu.htm

Jean Marguin, "The transfer interpreter and the birth of mechanical calculation."
La Revue, feb. 1993, n 2, p.26-33
http://www.cnam.fr/museum/Revue/Revue2/Revue2-6VA.html

Peggy Aldrich Kidwell, "Landmarks In Digital Computing."
http://www.nasm.edu/NASMDOCS/DSH/LDC/publicit.html

Mark Brader, "What was the first computer and who built it?"
http://kbs.cs.tu-berlin.de/~jutta/time/msb-chronology-of-dcm.html

Jones Telecommunications and Multimedia,
"Computers: History and Development"
http://www.digitalcentury.com/encyclo/update/comp_hd.html

Dr. Tim Bergin, Eric Ashman, Seth Gordon, Jeana Scheirer, Dave Muehling and Andrew Hewitt, "Mechanical Computing."
http://www.csis.american.edu/dept/research/history/office/

Rutgers University, "History of Computing - Calculating Machines." Outline.
http://www.rutgers.edu/Accounting/raw/gsm/!pa12sep.htm

E.M. Horsburgh, "Modern Instruments and Methods of Calculation."
http://moa.cit.cornell.edu/dienst/moabrowse.start-math/

W.G. Galle, "Mathematische Instrumente." (In German)
http://moa.cit.cornell.edu/dienst/moabrowse.start-math/

Libraries of Cornell University and the University of Michigan. "Manufacurer and Builder Journal."
http://moa.cit.cornell.edu/MOA/MOA-JOURNALS2/MANU.html

Andries de Man, "Original Documents on the History of Calculators."
http://www.geocities.com/SiliconValley/Horizon/1404/

Andries de Man - Internet Bookmarks on the History of Computing
http://www.dotpoint.com/xnumber/andries_refs.htm