Just a quick mention that the documentation Tom mentioned below for the SAXS tool in Chimera is a little out of sync with the daily build because the dialog is in the process of being modified. In general, however, the descriptions in that page and the FoXS page (linked to that page) will explain the options.

On Oct 15, 2010, at 4:26 PM, Tom Goddard wrote:

Here's a description from the Chimera
User's Guide of the Chimera user interface.

http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/saxs/saxs.html