The HRMA User's Guide describes characteristics of the Chandra High Resolution Mirror Assembly (HRMA), particularly those which may affect the interpretation of the imaging data. The detailed SAOsac raytrace model reproduces many of these, at least qualitatively; however some features are not treated adequately by the current raytrace model. For example, the wings of the PSF resulting from mirror scattering are known to be seriously under predicted in the raytrace model.