Documentation for setting up and managing a HEASARC-compatible CALDB is available from the CALDB Documentation Library. The information in the CALDB Installation, Maintenance and Use and FITS Calibration File Formats/Conventions sections is especially relevant to the Chandra CALDB.
ASC FITS Designer's Guide (PS, 40pp)
A. Rots and J. McDowell, 18 February 1999
CALDB Header Specifications (HTML)
A. Rots and D. Graessle, 06 June 2002
Chandra PSF Library (PS, 16pp)