... FOS Documentation / 29-2 . General Outline for Handling FOS Data / 29-3 . ... This part of the HST Data Handbook describes the basics of the FOS and is the main source of modern information for understanding, recalibrating, and analyzing FOS spectra. ... Chapter 29 gives a summary of the important sources of FOS information, apart from this handbook, a description of the instrument, an overview of the operational history and features of the FOS, and a brief introduction to FOS data-taking modes. ...