  WXM gives GRB localizations in instrument coordinates. WXM localizations must
be converted to celestial coordinates using spacecraft aspect information
obtained by the optical cameras on HETE. We must therefore accurately determine
the alignment of the WXM boresight with respect to that of the optical cameras,
in order to accurately determine the celestial coordinates of WXM burst
locations. We use a seven-parameter model that treats as free parameters the
three Euler angles of a pure rotation, two horizontal shifts of the
coded-aperture masks with respect to the detectors, and the heights of the
masks above the two detectors. We determine the alignment by fitting the model
to a set of 252 WXM localizations of Sco X-1 obtained between 23 April and 28
June 2001. We estimate the systematic error in WXM GRB locations by comparing
the actual and the calculated locations of Sco X-1. We find that the systematic
error corresponding to a 68.3% confidence region is 1.7$'$, and the systematic
error corresponding to a 90% confidence region is 2.4$'$. We find that this
astrometric solution also provides a satisfactory fit to an independent sample
of SGR and XRB events. These results are consistent with the astrometric
calibration and the systematic error in WXM localizations derived independently
using the RIKEN localization method.
