  We present the wavelength solution derived for the G800L grism with the Wide
Field Channel from the spectra of two Galactic Wolf-Rayet stars, WR 45 and WR
96. The data were acquired in-orbit during the SMOV tests and the early INTERIM
calibration program. We have obtained an average dispersion of 39.2 A/pix in
the first order, 20.5 A/pix in the second and -42.5 A/pix in the negative first
order. We show that the wavelength solution is strongly field-dependent, with
an amplitude of the variation of about 11% from the center of the WFC aperture
to the corners. The direction of the field-dependence is the diagonal from the
image left top corner (amplifier A) to the bottom right corner (amplifier D).
These trends are observed for all grism orders. We also describe the
calibration files derived from the SMOV and INTERIM data which are used by the
ST-ECF slitless extraction code aXe.
