This might seem a tad anachronistic to some, but fascinating nevertheless: Building a 5-ton mechanical calculator... from 19th-century plans.
http://www.networkworld.com/cgi-bin/mailto/x.cgi?pagetosend=/export/home/httpd/htdocs/news/2008/041108-difference-engine.html&pagename=/news/2008/041108-difference-engine.html&pageurl=http://www.networkworld.com/news/2008/041108-difference-engine.htm http://tinyurl.com/5ql8me Enjoy! Regards Steven Vincent Johnson www.OrionWorks.com www.zazzle.com/orionworks
