Editing Difference engine (section)

===Construction of two working No. 2 difference engines===
During the 1980s, [[Allan G. Bromley]], an associate professor at the [[University of Sydney]], [[Australia]], studied Babbage's original drawings for the Difference and Analytical Engines at the [[Science Museum (London)|Science Museum]] library in London.<ref>[http://csdl2.computer.org/persagen/DLAbsToc.jsp?resourcePath=/dl/mags/an/&toc=comp/mags/an/2000/04/a4toc.xml ''IEEE Annals of the History of Computing'', 22(4), October–December 2000].</ref>  This work led the Science Museum to construct a working calculating section of difference engine No. 2 from 1985 to 1991, under [[Doron Swade]], the then Curator of Computing. This was to celebrate the 200th anniversary of Babbage's birth in 1991. In 2002, the [[Printer (computing)|printer]] which Babbage originally designed for the difference engine was also completed.<ref>{{cite web |title=A Modern Sequel {{!}} Babbage Engine |url=http://www.computerhistory.org/babbage/modernsequel/ |publisher=Computer History Museum }}</ref> The conversion of the original design drawings into drawings suitable for engineering manufacturers' use revealed some minor errors in Babbage's design (possibly introduced as a protection in case the plans were stolen),<ref>[http://news.bbc.co.uk/1/hi/sci/tech/710950.stm Babbage printer finally runs, BBC news quoting Reg Crick] Accessed May 17, 2012</ref> which had to be corrected. The difference engine and printer were constructed to tolerances achievable with 19th-century technology, resolving a long-standing debate as to whether Babbage's design could have worked using Georgian-era engineering methods. The machine contains 8,000 parts and weighs about 5 tons.<ref name="CHM Press Releases">Press Releases {{!}} Computer History

* {{Cite press release |date=2008-05-05 |title=The Computer History Museum Debuts Charles Babbage's Difference Engine No. 2, On Display for the First Time in North America |url=http://www.computerhistory.org/press/babbage-engine-exhibit.html |publisher=Computer History Museum |access-date=2018-10-27 }}
* {{cite press release |date=March 31, 2009 |title=The Computer History Museum Extends Its Exhibition of Babbage's Difference Engine No. 2 |url=http://www.computerhistory.org/press/babbage-engine-extension.html |archive-url=https://web.archive.org/web/20160103015136/http://www.computerhistory.org/press/babbage-engine-extension.html |publisher=Computer History Museum |archive-date=2016-01-03 |access-date=2009-11-06 }}</ref>

The printer's primary purpose is to produce [[Stereotype (printing)|stereotype]] plates for use in printing presses, which it does by pressing type into soft plaster to create a [[flong]]. Babbage intended that the Engine's results be conveyed directly to mass printing, having recognized that many errors in previous tables were not the result of human calculating mistakes but from slips in the manual [[typesetting]] process.<ref name="Campbell-Kelly 2004" /> The printer's paper output is mainly a means of checking the engine's performance.

In addition to funding the construction of the output mechanism for the Science Museum's difference engine, [[Nathan Myhrvold]] commissioned the construction of a second complete Difference Engine No. 2, which was on exhibit at the [[Computer History Museum]] in [[Mountain View, California]], from May 2008 to January 2016.<ref name="CHM Press Releases" /><ref>{{Cite web |url=http://www.computerhistory.org/exhibits/babbage/ |title=The Babbage Difference Engine No. 2 |publisher=Computer History Museum |access-date=2018-10-26 }}</ref><ref name="chm2">{{cite web |author-link=Daniel Terdiman |last=Terdiman |first=Daniel |date=April 10, 2008 |title=Charles Babbage's masterpiece difference engine comes to Silicon Valley |url=https://www.cnet.com/culture/charles-babbages-masterpiece-difference-engine-comes-to-silicon-valley/ |work=[[CNET News]]}}</ref><ref>{{Cite web |last=Noack |first=Mark |title=Computer Museum bids farewell to Babbage engine |url=https://www.mv-voice.com/news/2016/01/29/computer-museum-bids-farewell-to-babbage-engine |access-date=2022-07-10 |website=Mv-voice.com |date=29 January 2016 }}</ref> It has since been transferred to [[Intellectual Ventures]] in [[Seattle]] where it is on display just outside the main lobby.<ref>{{Cite web |last=Boyle |first=Alan |date=2016-09-11 |title=Inside the invention factory: Get a peek at Intellectual Ventures' lab |url=https://www.geekwire.com/2016/inside-intellectual-ventures-lab/ |access-date=2024-04-21}}</ref><ref>{{Cite web |title=Intellectual Ventures on LinkedIn: #ivlab #coolscience |url=https://www.linkedin.com/posts/intellectual-ventures_ivlab-coolscience-activity-6568159438295965696-tGHx |access-date=2024-04-21 |website=www.linkedin.com |language=en}}</ref><ref>{{Cite web |last=Ventures |first=Intellectual |date=September 1, 2016 |title=IV's Favorite Inventions: The Babbage Machine |url=https://www.intellectualventures.com/buzz/insights/ivs-favorite-inventions-the-babbage-machine#:~:text=Visit%20the%20Intellectual%20Ventures%20Lab,in%20the%20IV%20Lab%20foyer. |access-date=March 24, 2024 |website=Intellectual Ventures}}</ref>