Surprised no-one has posted this, since it's calculator-related. A group associated with the Intel Museum has recreated the source code for the first product to use the Intel 4004 microprocessor, the Busicom 141-PF four-banger. The site has annotated source, as well as simulators for both the calculator and the 4004.
Click here to go to the site.
Best,
--- Les
[http://www.lesbell.com.au]