My suggestions of other web-sites on Mechanical Calculators :

The Rechenlexikon is "the" accepted standard in this field: http://www.rechnerlexikon.de/artikel/Hauptseite

A remarkable good technical web site is the John Wolff Web Museum : http://www.johnwolff.id.au/calculators/index.htm

Recommended web sites of German collectors:

• Restoration information is well provided by Prof. Dr.-Ing. Christian-M. Hamann
  http://public.beuth-hochschule.de/~hamann/calc/index.html
• Cris van de Velde http://www.crisvandevel.de/index.htm
• A nice site of Mr. Harald Schmid and links to others linke IFHB: http://www.rechenautomat.de/
  From his hand is also a comprehensive paper on memory mechanisms in mechanical calculators (used in the mechanical calculators who can perform the basic 4 types of calculation)
• The Robotron website is a very good, non commercial German site, with information of brands like ASTRA / Ascota / Daro / Robotron etc. these firms ones all belonging to the combination, in the former GDR, Robotron. Information is very well documented. It is a group of people working on providing information and keeping mechanical and electronic office machines machines a live. I give two entries:
  • http://www.robotrontechnik.de/index.htm?/html/menue/technik-computer-mechanisch.htm
  • http://www.robotrontechnik.de/index.htm?/html/computer/buchung.htm

Recommended web sites of Dutch collectors,

• Kees Nagtegaal: http://www.mechanicalculator.com/
• Tiny Henst: http://www.vintage-calculators.nl/

And don't forget these ones:

• http://www.rechenmaschinen-illustrated.com/
• http://www.ph-ludwigsburg.de/fileadmin/subsites/2e-imix-t-01/user_files/mmm/mmm_online/
• The nice made and very much appriciated information on MADAS machines by Gerald Saudan:http://www.madas.ch/
• http://www.officemuseum.com/calculating_machines_adding_listing.htm
• http://www.xnumber.com/xnumber/mechanical1.htm
• http://www.jmgoldman.com/index.php
• http://www.math.tu-dresden.de/wir/staff/ludwig/sammlung/sammlung.htm
• A link to the website of Professor Jim Falk (University Melbourne Australia). He's world wide know for environmental and climate change subjects, but at leased by me, until now, not well known as collector of counting aids. He wrote a book and a website, titled "Things that count".