Free42 is a software clone of the Hewlett-Packard 42S calculator. If you know how to use an HP-42S, you know how to use Free42. If you're new to the HP-42S and its clones, you may want to take a peek at the manual. You can get a scan of the original manual, wrapped in a rather large PDF file, by ordering the HP Museum CD/DVD-ROM set (highly recommended for any HP calculator enthusiast). Go to http://hpmuseum.org/ to learn more. Alternatively, you can get a free manual for the HP-42S and Free42 at http://thomasokken.com/free42/42s.pdf